I think you both are kinda of missing the main point to an extent.
It’s all about getting as many recurrent software purchases from your consumer base.
Having people on your consoles and locked into your ecosystem increases the likelihood of that happening.
That being said, as a publisher is doesn’t harm MS for selling their games on other platforms. But what they’re wagering on is that people will lock into their subscription service.
A lot of reasons, but my favorite is sony advertising like crazy that Harry Potter is a PlayStation exclusive due to one mission.