Well it also didn't help that Gears and QB ran like absolute sh*t when they first came out, partly because of v-sync restrictions and no SLI Support.
It might also be partly because Microsoft seems to be forcing their developers to make PC ports whether they want to or not. It's no excuse for putting out a bad product but I can see why the Windows 10 Store version wouldn't be a high priority when no one is shopping in that storefront. Any last minute polishing time is going to into the Xbox One version that people will actually play.
Maybe the shift to selling on Steam will help with that. For a lot of PC gamers Steam is the only platform there is. If a game isn't available on Steam it may as well not exist as far as those people are concerned. If Gears 4 also goes up for sale on Steam it will automatically sell many times more copies than it would as a Windows 10 Store exclusive so there would be a lot more incentive to make it work properly.