I think you're right, there is a barrier for most consumers who love Steam. But for another percentage of gamers, like me, there's zero barrier to entry.

1: I like not having to launch Steam to play my games.

2: I know there are good games that exist that aren't on Steam and am more than willing to go through a CC form or PayPal.

3: I'm slowly getting irrated with games with DRM, online-only, DLC.

I think itch.io is a win for these niches of indie game developers and consumers who buy indie games.