The classic tactic is known as EEE (Embrace / Extend / Extinguish).

It's not impossible to imagine a scenario where in the future, if the Fediverse is thriving, a seemingly good-intentioned corporation chooses to Federate its own instance on its own hardware. This opens up the capacity of the network even more and makes it more accessible and less intimidating to a broader audience. This is the Embrace phase.

Then comes the Extend phase, where they dedicate a lot of resources to improving their technology and platform and capabilities. They may add some functionality that is not defined in the ActivityPub standard, but it seems really cool or useful, and so a lot of people switch to it, and it becomes the de facto standard place to go on the Fediverse. Everywhere else is a ghetto that doesn't have Feature X.

Eventually, the corporate site, now the de facto, wants to continue to build on its capabilities, and adhering to an open standard is only a liability, especially given that the only people left on the Fediverse are unmonetizable weirdos. So they announce that they're going closed. The majority of people on the platform don't care because it's where most everyone already is. This, of course, is the Extinguish phase.

So yeah, it's certainly a possibility that could come to fruition. The kind of scary part is that to begin with, everyone could have the best intentions. But corporations are amoral and driven by profit incentive, and historically, that need to drive growth and profit has led to staggeringly similar decision-making (see Twitter and Reddit as examples of that). And so even if a company comes in with seemingly truly noble intentions, eventually the need to turn a profit has a high likelihood of leading to the fate described above.