Nope. No reason at all. They went out and acquired studios left and right pretty much for shits and giggles, because in reality they have no intentions of turning GamePass into the biggest service in gaming, or even if they did, they know that a steady stream of quality content independent of 3rd party reliance isn't particularly vital to that endeavor at all.
I should've specified that I meant rational reasons. Of course there are tons of irrational reasons to believe someone who promised the same thing 100 times and never delivered.
If you demand respect or gratitude for your volunteer work, you're doing volunteering wrong.