[balamatom]

>It's because people don't agree on what's better.

Or maybe, just maybe, it's because taste and discernment (which are personal values) correlate inversely with access to resources (which is a globally recognized value).

>It's a little silly to say "mainstream is crap! Why doesn't the better stuff rise to the top?"

If it's silly to ask that question, maybe it's also a bit silly to answer it - but sure, lemme throw in my own 2c:

It's because the "compromise" you speak of amounts to human society taking on the role of a half-witted hivemind.

IMO a better question to ask is what's the point of there being a "mainstream" at all? It's not like lived human experience is fungible... is it?