itch.io is doing fine, if anything i'm more worry about GOG falling because they too are a "walled garden". People talk about GOG all the time sure and they are with a big company, a company that has slowly been making games around 1 series that the author never plan to make more than 1 game with cycberpunk being their big thing and if that fails GOG fails since emplyess also aren't treated well. All of GOG games are paid which is understandable but they do not offer free games (no limited times do not count) which is why GOG has not beaten Steam.
I could go on but the ponit is that itch has zero problems, Gamejolt has a fandom problem also gamejolt never follows feedbacks, Humble Bundle reason it stay alive is by giving up and working with steam/IGN, and every other game store site that i know has a problem with promoting themselfs (itch.io is part of it).
I know itch.io isn't going away for a long a time people trust it more than any other store on the net. All the myth talk about "not getting enough views/buyers" is because those developers are new and like all new developers they do mistakes in marketing.
edit 2/26/19:
Omg i hate when i'm right: https://techraptor.net/content/gog-lays-off-about-a-dozen-employees