One medium where this isn’t really true is video games. Why hasn’t Steam or Itch fallen in this trap? Because they are honest stewards? Or because the software plane isn’t as large? Only news publishing and written word and movies. In fact movies even have a set number of prestige “risk” directors so they never have to reach too far out of the norm, see Yorgos Lanthimos.
But video games in general have fallen into that trap. There were certainly more variety in the mainstream/AAA scene in the 90s and 00s than there is now. No more major publisher really is in that mid tier wacky but interesting 6-7.5/10 game space anymore.
It goes back to the point that consolidation long term ends up being bad and the smaller/indie press is good for culture (and that is a big part of what Steam is, and I'd argue where the most interesting things in gaming have come from lately