I'll never understand why anybody would choose to buy a game from the MS Store. Unless you're into crappy games like Candy Crush or Solitaire. The way they package apps up and remove user control is beyond me.
That was the case when it first started and only continues as stand-alone. Ever since the XB1 the MS Store (GamePass) has carried more and more game titles available for Windows machines. They have good reason so a PC gamer can buy and then play it on his XB in a "play anywhere" title. I have the app on my gaming PC only because I have MSFS and it is a requirement for updates to the flight sim. There's nothing wrong with the interface though as I've seen just poking around out of curiosity. I find it about as user friendly as any other gaming portal.
In any event, I've been a PC gamer since the mid 1990s and have always either bought the retail box DVD version or when Steam came out, started downloading from there. I have never used the MS store and never will. In fact, I push everyone who asks me advice on new PC game building for the first time to avoid the MS store entirely and buy from Steam, direct from the publisher, or one of the Etailers like NewEgg which often run promos. Unless they have an XB1X and want to cross-play titles between platforms.