It seems as if all these tech companies's CEOs colluded and decided to do this at about the same time. I guess we can't call it conspiracy, if they haven't all flown to some remote island to play golf, and came back with this idea. But they can plausibly just watch and copy without others' behavior without actually coordinating with each other.
Real estate investment and the idea that large corporate share owners also invest in office real estate has been mentioned as the reason. But to me it mostly feels like a “soft layoff” tactic.
There were waves of layoffs already, but it wasn't enough, so they all noticed that RTC can be another kind of a layoff, and they don't have to worry about severance or inventing performance improvement plans and so on.
It's fascinating that they do it and have to lie why they are doing it. Nobody can say it out-loud. Not a single line in the internal chat or emails, especially no comment publicly. But everyone can read very well between the lines.