It is still a property they put down a lot of money for, as well as existing on competitor platforms before and after the purchase, so it makes sense to continue doing so. This is also why they can require an XBL sign in (optional).
Those previous IP's though?, they've existed with MS before the purchase of MC or Cuphead, so they tend to go with the Xbox identity, while MC, Bethesda and Cuphead do not.
Again, it doesn't make business sense to allow for a time, then pull them away. I like to think you think that's a brilliant idea, but I will have to give a hard disagree on that plan. Their ecosystem idea transcends this.
Minecraft is the only 1st party game IP that will continue to release on all platforms. None of the other studios MS recently acquired are doing the same thing except honor prior deals like Wasteland 3 and Psychonauts 2. If MS want to actually see the Xbox platform/gamepass really make strides, a constant stream on exclusive content is absolutely necessary. Continuing to release new games on Playstation won't help them see that growth.
I do see Fallout 76 and Elder Scrolls Online releasing on ps5 because these games are already on ps4 so why not keep that gaas money flowing.