I can imagine the following reasons for this:
- conflation of positive vs normative economics in macro
- micro phenomenon is less complex (or smaller): thus easier to create reliable models for
I used to think that microeconomics was relatively more scientific than macroeconomics. Early macroeconomics, in particular, suffered from a choosing models of agent behavior that made modeling easier but bore little relationship (or at least a highly disputed relationship) with reasonable behavior of individual agents. This led to the microfoundations effort, which attempted build macroeconomic models from the ground up by modeling the behaviors of the economic agents in line with microeconomic theory (rational expectations, utility functions, life cycle effects, market power, and so on). Aligning macroeconomics with microeconomics strongly implies that microeconomics "has it right" and macroeconomics does not.
However, that's not the end of the story. In a nice essay called The Macroeconomic Foundations of Microeconomics, macroeconomist Mark Thoma says that microeconomics has a lot of hidden macroeconomics lurking in the background, and it is important to recognize this and formalize the role of macroeconomics in microeconomic theory. For example:
One of the lessons from macroeconomics is that prices do not always move fast enough to keep markets in balance, and this observation -- this macroeconomic foundation -- needs to guide microeconomic theorists. The Walrasian auctioneer is a convenient theoretical assumption, somehow prices always magically move immediately to clear all markets and attain the highest possible societal welfare (and it's useful for comparing long-run outcomes). But that assumption is not very useful as a foundation for macroeconomic models that try to explain short-run swings in the macroeconomy. Microeconomic and macroeconomic models ought to be consistent with each other, but the microeconomic foundations need to have realistic assumptions about the ability of price changes to clear markets.
More generally, microeconomics usually assumes that microeconomic agents are embedded in a functioning macroeconomy. One with functioning markets for other goods, property rights, production functions and industrial organization that makes supply curves, demand curves that are well defined, and the like. This joint dependence on the assumptions of the other family makes the two major schools of economic thought closer to peers than the microfoundation revolution suggests.
That said, microeconomics has done a lot more to bring experimentation (field and laboratory) into their research. This has helped inform their modeling and econometric work in a positive way, including this year (2019's) Nobel winners. For ethical and financial reasons it is much harder to do this in macroeconomics. This could be a reason to think that, in general, microeconomics might be a bit more objective. However, the majority of microeconomic research is non-experimental, so we shouldn't go too far with this argument.
I also recommend Raj Chetty's essay Yes, Economics Is a Science for a comparison of the scientific bona fides of the field of economics with other scientific endeavors, particularly medicine.
It is true that the answers to many “big picture” macroeconomic questions — like the causes of recessions or the determinants of growth — remain elusive. But in this respect, the challenges faced by economists are no different from those encountered in medicine and public health. Health researchers have worked for more than a century to understand the “big picture” questions of how diet and lifestyle affect health and aging, yet they still do not have a full scientific understanding of these connections. Some studies tell us to consume more coffee, wine and chocolate; others recommend the opposite. But few people would argue that medicine should not be approached as a science or that doctors should not make decisions based on the best available evidence.
... Nonetheless, economists have recently begun to overcome these challenges by developing tools that approximate scientific experiments to obtain compelling answers to specific policy questions. In previous decades the most prominent economists were typically theorists like Paul Krugman and Janet L. Yellen, whose models continue to guide economic thinking. Today, the most prominent economists are often empiricists like David Card of the University of California, Berkeley, and Esther Duflo of the Massachusetts Institute of Technology, who focus on testing old theories and formulating new ones that fit the evidence.
This kind of empirical work in economics might be compared to the “micro” advances in medicine (like research on therapies for heart disease) that have contributed enormously to increasing longevity and quality of life, even as the “macro” questions of the determinants of health remain contested.
Those who decry the status of macroeconomics (to a certain extent), e.g. Krugman, do so because the macro field being closer to high-level political decision making is often involved in controversies, even if only a small part of the macro field itself is actually controversial (according to Krugman, 2013).
OK, here’s how I read the Gordon and Dahl results: what they show is that most of what economists do is indeed fairly objective and non-ideological; business-cycle macro, although it’s not at all like that, is a small enough part of the academic field that their data don’t pick it up.
Unfortunately, while business-cycle macro may not be a large part of what economists do, it’s a field that matters a lot – especially with the world still facing its worst economic crisis in three generations.
And then there's the "schools of thought" in macro. As an IMF blog summarizes:
Contemporary microeconomic theory evolved steadily without fanfare from the earliest theories of how prices are determined. Macroeconomics, on the other hand, is rooted in empirical observations that existing theory could not explain. How to interpret those anomalies has always been controversial. There are no competing schools of thought in microeconomics—which is unified and has a common core among all economists. The same cannot be said of macroeconomics—where there are, and have been, competing schools of thought about how to explain the behavior of economic aggregates. Those schools go by such names as New Keynesian or New Classical. But these divisions have been narrowing over the past few decades (Blanchard, Dell’Ariccia, and Mauro, 2010).
And that frankly is being kind by not mentioning a lot of the stuff "out there" that nonetheless influences some politicians, e.g. more recently Sanders or even Rubio and the MMT, Erdogan and the "neo-Fisherites" etc.
Personally, I never saw it this way. My background is in physics first, and I always viewed the micro/macro distinction as analogous to the quantum/classical distinction in physics. The point of macroeconomics is to describe the dynamics of bulk populations, which, due to constraints around information flows rooted in actual physics, are more efficient to attempt to manage through policy levers.
Micro gets you the deep, nitty-gritty observation of human behavior, but you can't actually do any meaningful experiments with a single individual. You always need a cohort, and then you end up talking about their bulk properties anyway, much like some of the more interesting results from quantum mechanics (e.g., the double-slit experiment).
The obsession with "micro foundations" for macro may make it sound like micro-economics is somehow superior, but I don't think that's the right way to describe the relationship. Also, to the extent that this analogy is valid, I strongly disagree that micro is "less complex".