Microsoft's moves the last few years haven't been carefully planned. They've been opportunistic moments. Zenimax wasn't going to shift anything. They needed a lot more than that. They needed a big mobile company. They needed big games to bump sub numbers. They needed a company that was huge in the PC space. ABK is all of that. Their legal troubles tanking their stocks was the perfect opportunity. They wouldn't have sold otherwise.
Not every company is up for sale. CD Projekt has made it clear they don't want to sell. Ubisoft does not want to be owned. Sega has said they're not interested. Even to buy T2 or EA, you'd have to offer their stockholders enough cash to the point where they didn't have confidence for the company to reach that number any time soon. And even companies like Microsoft have limits on what they're willing to spend. That much should be obvious in that they were outbid by Sony for Bungie.
The purchasing company has a value in mind. Microsoft isn't going to offer T2 $50 billion when their market value is only half that. It would be an absolutely boneheaded offer. Also, the more they buy up, the more likely they are to run afoul of regulators. They've already had a hell of a time grabbing ABK. A future purchase of another massive publisher will likely face increased scrutiny compared to what it would have had ABK not been bought. It doesn't guarantee a block, but their previous purchases will be taken into consideration.
It also depends on moves made by other companies. Like it or not, we're in a consolidation phase. There's going to be more purchases. Tencent just made another move. A small one, but a move nonetheless. They already have their claws partially in Ubisoft. Embracer had been buying things up. Sony might as well be shouting from the rooftops that they're going to be spending even more money to own things. Based on their comments as of late.
It might seem shitty, but it's a snowball effect. One thing leads to another, leads to another, leads to another. Each step for one company justified by what the others did before. The upshot to this industry is that it is very resilient to too much being owned by one company. There are a ridiculous number of startups with good funding and a lot of talent popping up these days. Many of them displaced from the very consolidation some fear, with others having formed from the dying husk of companies already owned.
Truthfully, the only way Microsoft runs away with the industry is if everyone else just stands still. That's not going to happen.