I've recently started my PhD and upon looking at my textbook (the sargent one) I found that it differed greatly from my Masters textbook (Romer) and in turn my undergraduate macro text (williamson).
What is perplexing is that for the most part the models taught in all three books deal with key questions of economic growth, labor markets and business cycles. However the approaches are very different and dont necessarily feed into eachother almost like each model stands on its own disregarding the method of the previous.
This is not my experience with micro, where it was very clear that more and more depth is uncovered using the same core models of consumers, firms and market structures.
This all being said, though i recognize the value of being exposed to so many different models as part of my academic training, holding them all on the same scale when analysing a phenomenon can be at times contradicting (i.e comparing the insight from infinitely lived households to overlapping generations models).
Bottom line: why are there so many different macroeconomic models that explain the same phenomenon.