why is it that artists like these can write what is widely regarded as some of the greatest music ever written, and then once they pass a certain age or get a certain number of zeros in their bank account, they lose their ability to know a good tune when they hear it?

do they lose their drive to write soulful tunes when they are rich enough to own a diamond encrusted bog brush? or is it that they set themselves standards that are too high because of the quality of their older stuff, meaning that pretty much anything will look pretty pale in comparison?