Art is the production of veblen goods. Duchamp, in his genius, realized that though the ability to buy something painfully handcrafted does signal wealth, buying literal garbage is a much better display of wealth. Someone who can afford to buy a meticulously painted portrait, well, one may be will willing to make sacrifices for beauty. Someone able to spend millions on literal garbage - now that is a rich man.

Another aspect is photography allowed normal people access to create cheap reproductions of beautiful art. High-class people used to be able to distinguish themselves from the mob with beautiful things the mob couldn't afford.

But this does not work with cheap reproductions allowing one to signal the same taste.

In this way, there became an incentive for high-class people to acquire and inculcate a taste for art that is actively repulsive to distinguish themselves from those normal people who desire beautiful things.

Mostly this doesn't matter. They are only hurting themselves. But the effect of these incentives on public architecture has been pretty horrifying.