Re: So ?
No software runs exclusively on Windows. Alan Turing wrote proof of that. The only issue is whether the cost of migration between runtime platforms is greater than the cost of staying.
It's a little more complicated than that, because runtime platforms aren't all created alike. For example, some game developers have abandoned macOS because Apple's 3D acceleration APIs have fallen behind (for example, they don't support OpenGL 4.3.) This leaves them the choice of either crippling the other platforms in order to dumb them down to macOS's level, writing a lot of duplicate code in order to support a macOS version of the game that will never perform well, or dropping macOS support.