To be clear, I’m not complaining that we don’t have these aforementioned applications on the Linux desktop. That’s not the point. The point is “we” still don’t have a robust way for developers to monetise their application development work.
Most desktop Linux users run Ubuntu. Followed by others you’ve likely heard of like Arch, Fedora, Manjaro, SUSE and friends. Most users of these desktop Linux distributions have no baked-in way to buy software.
Similarly developers have no built-in route to market their wares to Linux desktop users. Having a capability to easily charge users to access software is a compelling argument to develop and market applications.
For sure, I can (and do) throw money at a patreon, paypal, ko-fi or buy a developer some coffee, beer or something from their Amazon wishlist. But I can’t just click “Buy” and “Install” on an app in a store on my Linux laptop.
Maybe one day all the ducks will be in a row, and I’ll be able to buy applications published for Linux, directly on my desktop. Until then, I’ll just keep looking longingly at those macOS app developers, and hoping.
And because it has a standard set of libraries, it's probably the closest thing to a stable, cross-Linux-distro binary target out there, which I suspect most closed-source software would just as soon have.
You run your open-source stuff on the host distro, and run the Steam stuff targeting the Steam libraries.
Well, whoever does that for closed-source software is going to basically have to do what they have done. Probably some kind of cross-distro fixed binary target, client software to do updates, probably some level of DRM functionality like steamlib integration.
If it's not Steam, it's gonna be something that has a lot of the same characteristics.
Personally, I kind of wish that there was better sandboxing for apps from Steam (think what the mobile crowd has) since I'd rather not trust each one with the ability to muck up my system, but given how many improvements Valve's driven so far, I don't feel like I can complain at them for that. A lot of the software they sell is actually designed for Windows, which isn't sandboxed, and given the fact that not all the infrastructure is in place (like, you'd need Wayland, I dunno how much I'd trust 3d drivers to be hardened, you maybe have to do firejail-style restrictions on filesystem and network access, and I have no idea how hardened WINE is), it'd still take real work.
Their use of per-app WINE prefixes helps keep apps that play nicely from messing each other up, but it isn't gonna keep a malicious mod on Steam Workshop or something from compromising your system.