Weirdly, I feel like it's hard to get organic traffic / supporters/ followrs from Gumroad itself, whereas Itch's community spirit and interactive nature fosters more engagement and, if nothing else, lots of organic traffic on your page. Maybe there's another dimension to GR that I'm not privy to, but it seems more like a "Here you go, you're on your own!" type of experience and Itch is way more warm and inviting in comparison.

I also found this thread on a Google search, I like that it's not even that old yet. Great minds think alike!

I use both, plus also Artstation, Payhip (which is similar to Gumroad) and GameJolt (something look-alike to itch)... honestly, I've found not such great difference in finding quality interactions, but every other shop has far more tools to manage your project's contents and distribute them in packages than itch...