Gamepass on PC is a side effect not it's goal. The only reason you get to use it is because of the few Play Anywhere titles. This is a separate thing that will be fully catered to PC so we'll get 100+ games including stuff only on PC vs just a few games that happen to have UWP versions on the Windows Store AND are play anywhere on GamePass.
Even then it's still pretty bad, i can't get We Happy Few to play or download anymore after it initially used to work.