Which is funny as Stan Lee NEVER hid the reason he invented it... He just got tired of writing origin stories and wanted an excuse for people to have powers from the get go.
I don't think we're going to bother explaining the X-Gene because it's so inconsistently explained in the comics. The only thing you need to know for our game is that the X-Gene is a thing that exists, there are some individuals who can turn it off and unless you're some of the unlucky examples shown post M-Day, it just stops you from using your powers.
Any actual lore discussion beyond this I ask be taken to the off topic thread.