Major League Baseball has been around for years and just like any other sport game franchises like NBA, F1, FIFA and so on there is a video game associated with it or even movies as well. The game itself is simply MLB The Show and has been under Sony’s wings for a while as a console exclusive.
Around the time when Microsoft was approved for Bethesda acquisition, MLB’s contract with Sony has sadly ended. Staring MLB The Show 21, MLB went on a multi-platform deal which allows the game to release across different platforms like the Xbox. I think this is MLB’s own decision to release the game on multi-platform or else MLB threatens to withdraw from the exclusivity all together at least from what I’ve read on the Internet. Is kind of like how the Yakuza series left Sony and become a multi-plat game.
When the game was first announced to be on Xbox Game Pass, people thought Microsoft has to do with all of this right after the purchase of Bethesda and also more planned game studio purchases according to rumors. No is not. Microsoft may have worked behind the scenes to help optimize and port the game and bring the game to Game Pass, that’s pretty much it. You can even see the tweet above for yourself. Even with the trailer people are going ape shit and thanking Microsoft lol
The game will be available on April the 20th on PS4, PS5, Xbox One, Xbox Series X/S.  No PC as of yet.