This is the tragedy of the decision. As a PlayStation only gamer, I'm not shedding tears for Sony. This deal would be just as shitty if it had been them trying to buy ABK instead of Microsoft. What we've seen happen pretty much around the world is that regulators and courts have now weighed in that there is nothing anti-competitive or anti-consumer about a platform holder buying out a major segment of the industry and potentially locking its content behind their own iron curtain. Microsoft has made "pledges" to keep ABK content on PlayStation and to bring it to Nintendo. But there's no legal obligation for them to do so and let's be brutally honest. MS can afford to leave the many, many billions of dollars on the table by locking Sony out of the content. Sure, it would be very expensive, but they can afford it and may very well see it as the cost of doing business, long-term. Their goal, like any player, is to make their competition irrelevant if not force them out of the space altogether. Anyone thinking Sony wouldn't love to do the same is kidding themselves--the only difference is Sony does not have the resources to push Microsoft out. Microsoft can buy and sell Sony dozens of times over.
Regardless of what MS does or doesn't do with ABK content, the real story here is that legal precedent has now been set. It will be much harder for regulators to bring suit or seek injunctions against further acquisitions from any players in the space, even Microsoft. There would need to be proof that allowing the acquisitions would create a monopoly. Typically, when courts and regulators fail the public in this spectacular a fashion, the only restitution is after the fact. The monopoly is actually allowed to occur, and then government decides "hey wait a minute..."
You can expect a lot of buying out across the board from all sorts of players at the first and third party level, mass-consolidation and very likely attempts to setup iron curtains as platform holders seek to defend themselves. "Oh yeah? Well if you don't give us Game X, you won't get Game Y!" There's a nasty mess coming, and the loser won't be Sony, it will be gamers everywhere.