It’s all about anticheat support. The game would likely run on a Linux desktop, but Epic chose not to support Linux devices. They officially said (I have no source to link to it at hand) that they don’t believe the anti cheat would work well in Linux, because it lacks root access. On Android on the other hand they have a better sandbox and control. But most importantly, on Android they have a wider audience and that is basically all it counts for them. Epic CEO Tim said, if the Steam Deck gets sold enough, they will consider it.

I’m just listing what has been said, not sharing their same opinion.