They need more developers in house to ensure that the content doesn't leave the service. This is why you saw them go on a spending spree a year ago and why I believe they are not done.
As a person who predominately enjoys contained single player narrative games, I expect at least two or three of these kind of games from Microsoft a year within the next couple of years to ensure that I'm essentially getting my money's worth. At $15 a month, you are looking at a full priced game at $59.99, once every four months. I could purchase three single player games at launch that are also launching into the service, or I could pay for a service that allows me to try some other types of games I normally wouldn't play.
I would say they need close to 36 separate development teams to ensure that almost every single month a new first party title will be entering the service. (Obsidian has three, ninja theory has three, Double Fine can crank out a game a year once Psychonauts 2 is done so we can say they have three, Playground has two, and Rare has at least two)They have essentially 24 development teams now. I think an acquisition of WB Games would give them approximately 11 new studios and TT has several development teams. Not every experience needs to be AAA, but to ensure that people stay on the service you need to make sure the content continuously comes and that it stays. If they add WB and continue to work with smaller developers and ensure their games launch on Game Pass you are looking pretty set for the foreseeable future.
