[cjmb]

The book cover thing is really insane, too. It's gotten a little better over the last decade, but the early 2000s period was crazy (source: moved from UK to USA at that time).

It's interesting that your pet theory is New York City parochialism. Mine is gerontocracy: the (mostly New York based) publishers of SF & Fantasy have been run by the same aristocracy for ~70 years. And those folks cut their teeth on serialized pulp fiction, comic books, and magazines, which culminated in a certain art style that (imo) peaked in the 1980s.

If you browse wikipedia, you will see that many, many, many roads lead back to: https://en.wikipedia.org/wiki/Ace_Books

Outside of the US market, newer publishing shops were started & run by younger folks with more modern artistic visions.