Even if the argument is that they aren't making games for some franchises, Microsoft could still hire them to make games for different franchises as an exclusive, without acquiring them.
They aren't making games for most of the franchises they own. Current market forces certainly aren't inspiring them to do so. Contracting them to make a new Metal Arms, for instance, means they're allocating personnel away from their money makers, which raises the price of that contract to make up for the opportunity cost.
Yes it would be good if Playstation had more competition from XBox, but I have absolutely no confidence that they will get there just by acquiring publishers.
I have absolutely no confidence that they'll get there without it. And to be clear: I hate that. I hate that when Sony gets an exclusive game, it means I have to wait two years to play it on PC. I hate that my friends hate the new PS5 controller but have to use it because that's where you play God of War. But exclusives dictate a console's success, as much as I wish they didn't. So even if Xbox has quick resume and doesn't arbitrarily make its old controllers incapable of working on newer games that don't use the new controller features like Sony does, two friendlier features in the Xbox camp that would influence a purchasing decision in a perfect world, the customer is hardly ever going to pick Xbox, because the market decided exclusives matter that much.
They already acquired Zenimax/Bethesda and Redfall turned out to be a disappointment.
A game that was in production for a long time before it became a Microsoft product.
Sony is making God of War and Last of Us with their own studios, they don't need to buy exclusivity for that.
There is no functional difference between this and buying other studios, especially since Naughty Dog was also a studio acquisition. Given enough time in the rearview mirror, Activision-Blizzard and Bethesda games will be treated the same way as you just treated that one.
What is Microsoft making? What good would it be to let them have even more publishers and franchises?
We just saw a ton of games that they're making. And games these days just take so much longer to make, at least at the scale that Microsoft, Sony, and very few other companies insist on making them. Rocksteady has been working for 8 years on one game. The average AAA game has a 5+ year dev cycle now, which is absurd. The next game from Sony Santa Monica likely won't come out until there's a PlayStation 6. The likes of InXile, Obsidian, and Double Fine will have quicker turnaround times than most, and even those will take 3+ years. So with that perspective, the Microsoft acquisitions are fairly recent and are only soon going to start bearing fruit like Hellblade; not even Starfield counts in that discussion.