This does not meaningfully follow. What you "want" is orthogonal to the responsibility of the vendors of software.
The OS should protect where it can. So should software, lest your networked game nuke, say, the parts of your home directory to which it has permissions because without those permissions it can't do something it needs to.
This is just defense-in-depth. It's super basic stuff and HN is literally the only place I see people galaxy-braining about the idea that you have an obligation to not write shit code.
I suspect GP's point is that a networked game should be limited in access to only parts of one's home directory relevant for that game (that is: the game's own save data or configuration files or what have you). It is absolutely the job of the operating system to provide that sort of sandboxing/isolation.
The OS should protect where it can. So should software, lest your networked game nuke, say, the parts of your home directory to which it has permissions because without those permissions it can't do something it needs to.
This is just defense-in-depth. It's super basic stuff and HN is literally the only place I see people galaxy-braining about the idea that you have an obligation to not write shit code.