The Gamepass Ultimate requirement came like 2 years ago before they transitioned to a multiplat publisher. A result from bad game sales from Gamepass cannibalism. No surprise here, I never buy their games on their store, only on Steam. They could in theory remove that requirement now that they have 75+ more customers with no Gamepass option, but they looooove money so we'll see.
Them releasing their games on more platforms doesn't affect anyone who're already in their ecosystem. No more than PC ports of PlayStation games. There is no negative effect really, not yet. Quite the opposite it could be a positive thing if their games become more popular from more people playing them and make them pop up on sales top lists and talking about them and fill up mp servers and vote for GOTY awards etc etc. This snowball has only just started moving. Besides Minecraft their games has never had a userbase this big before so who knows what will happen.
Eventually little market interest in their own console will lead to devs not bothering doing Xbox versions, but one step at a time they're not there yet, except from Series S which has been a problem from day 1.
Once they stop manufacturing the console, once they stop releasing games for it. Then they've abandoned it.