As Kitsune rightly points out the usual reason for the inclusion of the time preferences for money into the discount formula (or Ramsey fomula) is that we observe this kind of behaviour in people. Given that many economists take a positive approach towards the study of economics, that is a logical stance.
That being said the last word is not spoken on this, and discounting and its use in benefit cost analyses for especially long-term policies is an active area of research. The Stern review on the economics of climate change sparked intense debate on whether we should include a pure rate of time preference and if so, what its size should be. On the one had you had economists like Stern who argued for a very small rate (0.01 % if memory serves), only to account for catastrophic risk, on the other hand there were economists like Nordhaus who argued for a rate close to 3%, based on observed choices by people in real life and the interest rates. Wikepedia covers the debate here
Martin Weitzman did a study among 2160 economists what the real discount rate should be for climate change (that is pure rate of time preference plus discounting because of GDP growth) called Gamma discounting and published in the AER. He found a range from -3 to 27%, which may give you an idea of the disagreement among economists on the issue of discounting.
Drupp, Freeman, Groom and Nesje did a more detailed follow-up in 2015, called discounting disentangled. Their range for the full discount rate is lower, from 0 to 10%, and they also asked explicitly what the pure rate of time preference should be. The mean recommended value for the latter by their 200 surveyed experts was 1.10%, but even that rate had a range from 0 to 8%.
Interestingly, the person who first came up with the Ramsey formula, Frank Ramsey, in a mathematical theory of saving, argued for a rate of time preference for societies of 0, calling a positive rate "ethically indefensible", although he does use a positive rate later on in the paper.