Microsoft aren't selling them. It's 3rd party companies. If you're a Flight Simulator fan this is an average price to pay for these planes.
Microsoft Flight Simulator has its own store where different companies sell these aircrafts. Dedicated Simulator fans will buy them.. This isn't aimed at you, the casual gamer.
I guess you've never played a Flight Simulator before? These are 3rd party add ons with complexity configurations. Each planes are basically different gameplay.
It takes 100s of hours to model these planes like real life.
I don't want to limited to one platform. There's a new Quest that's scheduled to be released this year or next year... Quest isn't limited to one storefront unlike PSVR 2.