It seems so unappealing that I'm surprised that it's even as high as 2%.
Microsoft's reason for selling games on the Windows 10 Store is to promote the Store as a successful marketplace. Making any money off these games is only a secondary goal at best, so I doubt that we'll see any of Microsoft's big games on Steam any time soon.If their titles aren't selling as well then they better hurry or else they are just losing lots of potential cash.
I don't even think PC gamers have an issue with buying MS made games, it's more of an issue with the store itself that people are avoiding in it's current state.
Though I suspect that the decision is more than Phil Spencer call.