> Is it just the CEO Zeitgeist?

This is quite likely a big part of it. There's a lot of herd behavior in the financial markets. A few companies fire a bunch of people, stock price goes up, others follow suit.

Also, in many cases, this isn't something that anyone pays attention to on an ongoing basis, because very few execs have the mandate to do it at a large scale, and their attention is scarce. So in practice, it tends to be done at intervals, and doing it when other companies are also doing it gives cover.