Not to mention Valve's effort with Proton, allowing non-Windows gamers enjoy what they pay for on multiple platforms with great ease; their efforts have been massive for gaming on Linux, and without it, I wouldn't have paid for a lot of games, earning their developers a whole lot of absolutely nothing.

Also the community hub, the workshop, the review system, the cloud saving, the functional wishlist, the gifting system, the shopping cart, the anti-cheat (you're better of with it than without it), the discovery queue, the sales dedicated to specific types of games that actually help people discover games and drive the revenue up for the developers, the (I think) complete transaction history, the refunds system, the friends and the chat and profiles - and probably many more things that I'm either not aware of or couldn't list off the tip of my tongue, combined with internal works that, again, do help the devs in the end.

Steam is much more than a place where one pays for a game to then simply download and play it. It's much greater and more functional than that. None of the developers have to put their games on Steam - nobody forces Epic Games Store or GOG to be this subpar in comparison. Same way nobody forces gamers to use Steam. People use Steam because they love it - or because there's no good-enough alternative, but that's hardly Valve's fault.

Steam charging 30% is not just worth it, but also surprising, given what putting your game on Steam gets you as the developer, and what it gets us, the players.