Wasnt this blatently obvious already?
Mostly, but not completely.
Bethesda is still a publisher, with its own properties to exploit and finances to maintain. It is now also a part of Microsoft, and has a benefit to working with its parent company for the larger benefit of the conglomerate. Xbox will have all of its titles (although Bethesda is still also making mobile titles,) and in general cases, that working relationship and the premiere status of the Bethesda name in the Xbox community will be the best way to launch new products. However, the door was never officially closed to the wider world, and for reasonable reasons. For one thing, there are likely some deals (even all this time later) which may make them publish for other platforms (Indy is one of the big questions.) But more than that, there's possibly more money to be made selling certain titles on multiple platforms than there is selling to only Xbox gamers (and moving Xbox consoles and gaining XBGP subscriptions and everything else that gets factored into that decision.) Microsoft can tie down exclusivity for the brands which would really make an impact as exclusive to their ecosystem, but they're getting all these games on Xbox Game Pass anyway, which is the primary reason why they bought the company. Mission accomplished already, so if there's extra money to gain or a greater subscriber base to build from releasing product elsewhere, (maybe after time-exclusivity, maybe day-and-date, depending on the product,) so long as that doesn't de-value the property's position in the Xbox slate, that may be an avenue worth exploring.
These days aren't like the old days, where the exclusive games you had on your box determined the value of your box; now the biggest games are multiplatform and most everything on either console is/will be on the agnostic PC and certain brands made in-house get released on other consoles. There's still that battle (we won't be seeing Halo on PS any time soon, nor God of War on Xbox,) but it is not what the war is being fought over. Subscriptions and franchise commoditization are what they're really after, and there are many ways to score a victory in that campaign.