This is more of a history of science question, but I hope it's on-topic here.
I've read that Thomas Bayes only managed to discover Bayes' theorem for the special case of a uniform prior, and even then he struggled with it, apparently.
Considering how trivial the general Bayes' theorem is in modern treatment, why did it present a challenge for Bayes and other mathematicians at the time? For comparison, Isaac Newton's Philosophiæ Naturalis Principia Mathematica was published 36 years before Bayes' main work, which was published posthumously.