This is not a conspiracy theory, even though what I'm about to say will sound like it. If you can talk to someone from the exec class in confidence (which unfortunately may require a close personal relationship or high trust), they'll tell you there was a clear -- if somewhat tacit -- understanding that the job market had gotten too hot during Covid and something "had to be done" about it after ZIRP ended.

Elon's layoffs at Twitter were basically the signal for the rest of the industry that it's time to reverse the trend.

Responding to identical market conditions in similar ways based on input from overlapping shareholders does not require collusion between execs.