I do not understand this.

I get that it is difficult to find good games on many other platforms, but once finding one, why do people not want to buy the game from them? Surely once you have given your details to a platform to buy one game, it becomes very easy to buy another. In my mind it is more convenient to simply download a game and have the installer forever, rather than needing some application always running to do the same thing, and to run the game.

On top of this, there are other games stores more similar to Steam, which don't get any traction.

Because Steam was the first big successful marketplace for digital games, so now people believe that's how a "real" game marketplace is supposed to look and work. That no other way is possible. And nobody else can be a better Steam than Steam (obviously), so people turn their nose at alternatives, and the gap keeps growing. Sounds familiar? It's what Microsoft did with their monopoly on operating systems and office suites. Or Adobe with graphics apps.

I think most people also do not care that much about the whole drm thing and have no problem just installing what is mostly known and used for pc gaming nowadays. The same way also a lot of people do not mind installing every launcher the publishers throw at them. I am open for other options if they make sense, but what we have for game launchers at the moment strikes me the same way as the billion streaming sites every company owner wanted a bite of the cake from. It can be bad to be on both sides of the scale, I would say.

Itch.io not only has no drm, but is rather more niche. There are a lot of thoughts going into publishing on "yet another" storefront for a developer/publisher, so unless it hasn't been forced onto you or gained somewhat mainstream appeal, most will not use it. GOG is another good example: It wasn't known that well unless you specifically looked for a good site to find old (and working) games. Since then it became wider known, partly because of the company behind it, partly because it expanded to also include new and indie titles. But still, it is mostly a question if "new game xyz" comes to the platform, either because the publisher doesn't want to tend to an additional platform and calculate the profit, alongside having to take care of another (drm-free) build, or because the game is already stuck  on one of the other publisher-owned launchers, among it just not being that publicly used compared to steam/consoles. Which looks like a self-repeating cycle at that point.

Next you ask why people only upload their videos to Youtube.

It is true and not quite true in both cases.

Not all people want to use only Steam. But it is just so big. It is the defacto playstore of deskop pcs. Just like there are other playstores on Android. If it is a serious (pc) game, with publisher and all, and not on Steam, people gonna wonder what is wrong with the game.

im just happy we have at least 2 platforms which are truly wonderful places with with strong communities pushing the limits of video gaming.

both steam and itch are unique, amazing and totally worth taking part in IMO. i want to experience both.

tbh i dont use any other ones, used to use GOG.. always liked that when i had a bad PC so old games were a blessing ( cool community).

if you ever feel like your not meant to be here or on steam just look at the top charts for games on google play. ITS HORRIFIC lol