Here's another simple explanation: Sticking out makes you a target.

People in 1024 -> This dazzling new cathedral is a testament to the majesty of God and a point of national pride.

People in 2024 -> This indulgent new cathedral is made from the exploitation of the masses and is a symbol of a something-phobic regime. Seize their assets!

This also works on an individual level, especially online - being novel makes you a target, so instead everyone chooses to be boring.