We need to evolve the terminology. The games on Itch.io are not Indie games - they are sub-Indie. Mostly amateur, hobbyist and school projects.
People who are making games as a serious side-gig or full-time job (ie. the typical definition of Indie) are all on Steam, and the best Indies are on console and Epic Games Store.
People want curation and less junk on Steam. Itch.io is exclusively... uncurated junk.
I think Itch.io would thrive if Steam increased their listing fee (Steam Direct) to $2,000 and required $100 annually if the game generated below $2,000 of gross revenue. This would be great for Indie games and consumers on Steam, but would give Itch.io an opening on the low end, so its probably why Valve isn't doing it. Ironically they are pushing their own top customers (and suppliers) to Epic with this strategy though!
I think Itch.io would be better with some kind of very cheap subscription, or being supported by advertising or sponsorship (integrated into game distributables). It could be like the Newgrounds of the next generation. It should be the place where you can try out low-end games for very little costs, secure in the knowledge that the executable has at least been verified for malware.