It's usually not that it isn't supported at the kernel level, it's more likely that the game developers choose not to enable it. BattleEye and EAC both work on Linux just fine with certain games and have no issues. Others like Fortnite and Destiny 2 are willingly making the choice to exclude Linux.
If you don't believe me, look at the list of games that run on Stadia that don't on Linux. Stadia servers run on Linux, and many of the "Windows Only" games you see were available there, including Destiny 2. BattleEye and EAC have even come out and said as much. They said they've offered to work with the studios to enable Linux support and the studios declined.
To tomscharbach point, this could be related to market share. More likely though in the case of Fortnite it's tied directly to the desire to drive all financial activities through Epic games and not third parties like Steam, Google, or Apple.
