it seems a bit pointless

Quite the opposite. Linux is currently frequently matching Windows in performance when running games through Wine/Proton. Targeting Linux native avoids this translation layer, and can result in better performance or less CPU overhead for the same performance (which is noticable especially on devices like the Steam Deck).

making games for Linux is ironically difficult

Yes, because of the tooling. If you make a game in Unity, and build for Windows, ““things just work””. If you then build for Linux, you can face any number of random engine issues, like bad controller support, broken mouse grabbing, etc.

as they can break as libraries change over time

Valve has thought about this, and designed the Steam Linux Runtime. This does effectively the same thing as Flatpak, except it pulls in the system native graphics drivers. Steam Linux Runtime provides effectively a full (minimal) Linux distribution that game developers can target, ensuring their games keep running, even on more modern systems.

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Gaming on Linux has always been a chicken and egg problem. Gamers see there’s no games on Linux, so they stick to Windows. Developers see there’s no Linux gaming market, so they stick to Windows. With Valve’s Proton, they interrupted this cycle. Most games now work on Linux, but game developers haven’t switched yet. For them to switch, there needs to be a market of Linux users, and the tooling needs to be sufficiently developed for Linux, ensuring the same (or better) quality as the Windows versions of games. This includes game engines, common libraries (like online multiplayer frameworks or voicechat), and possibly development software, 3D modeling software like Blender, the Adobe suite, etc.