Apple is completely different and outside of MacOS strictly controls everything.
Not true. Steam has a lot of DRM-free games that can be bought on Steam Store and are typically started through Steam client but do not really require Steam to be running. They're simply not integrated with Steam in any way.
For offline games, the DRM is little more than an anti-(casual-piracy) feature, making the obvious copying of the game folder not work, with generic cracks being easy to get online. It is more like games requiring the disc to play back in the day, even when fully installed, as a measure to avoid casual piracy, especially before CD writers were a thing.
Interestingly, despite having a generic executable wrapping system, many games that choose not to use Steamworks DRM are the older ones where source code is no longer available to recompile, or there are concerns about recompilation. I’m not sure why the wrapper would be a problem, unless the games contained integrity checking code, or you want compatibility with modding tools that edit the binary. Alledgedly at least one publisher literally applied a crack they downloaded from a piracy site to their retail release, and uploaded that to Steam, and in that case, I could easily see the steam DRM wrapper not being feasible to apply, as residual checks from the old DRM could cause breakage.
Valve even went out of their way to conceptually decouple the SteamVR SDK from steamVR. Instead they made “Open VR”, an interface conceptually like OpenGL or Vulkan, which allows for more than one runtime implementation. However, SteamVR is the only runtime implementation. But in theory, if a VR game on steam did not use Steam or other DRM, and you had an alternate OpenVR runtime, you could take the game folder from Steam, and run it against said alternate runtime fully separate from Steam (if only such a runtime actually existed).
Steam’s competitors like GoG also take 30% so maybe it’s a reasonable price for the service they provide? Only companies like MSFT or Epic can charge less since their stores are heavily subsidized.
Of course as long as games remain available on multiple storefronts it will remain a winner takes all market and Steam does have a significant moat (though not in any way comparable to Apple) due to it’s social features.
At the end the existence of Steam/(other centralized storefronts) seems to benefit both consumers and developers compared to any alternative option (less risk for consumers = higher long term revenues or developers)
Anyways, it looks like my point made it across.