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.
They had opened a lot of studios and even TV/Movie ones this gen and we didn't see anything but closures.
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"