The idea of MS moving their games to be services is hilarious given they have absolutely no staying power with pretty much anything.
The thing with the above is that MS really does try and put in a ton of effort for their games to be well, service-like. Halo 5 gets great updates, Killer Instinct is great and Forza's content and polish is always top-class.
But even ignoring the fact that there's been a drop-off in popularity for some of their games, their cycle of new releases and products are too frequent to really transition to a service-platform. They're no annual franchise company, but there are enough in a single generation to... well, muddy the waters.
Of course some games can do so without any problem. Have the cake of releasing multiple numbered titles in a single gen and maintain the longetivity of being played by millions for the entire console lifecycle and beyond that. But it's tough. Market is super competitive even in the space of "most played games", and even those games aren't as successful as the evergreen behemoths.
And the really successful service games are ones that are evergreen. Nobody's talking about DOTA3, Minecraft 2 or League of Legends 2 because those aren't in the vocabulary of expectations for fans of said games.
One of the few question MS needs to ask itself if it really wants to transition into that super difficult world, imo is...
"Are they comfortable with releasing only one flagship Halo/Gears/Forza game for an entire generation, and supporting that for the rest of a single lifecycle?"
I feel like that is a line that is very very difficult for MS to dare to cross, because ultimately they're in a business of selling consoles and unless you're an evergreen title, you aren't charting forever.