Not only the extremes, also the speed: good employers can turn into bad employers (has the opposite ever happened? I'd love to learn of an example!), but big companies at least have some inertia while it happens. There's probably even some "Sun" still left, all those years after the Oracle takeover. Compare this to what happened at Komoot.
Founder(s) sold to Bendinggspoons who specialize in the kind of takeover where the buyer stops all development and tries to keep the money inflow from a service running with minimal maintenance crew. Evernote is the most famous example I think.
Apparently 80% are already gone:
https://escapecollective.com/how-komoot-lost-its-way/
(paywalled, but I think it's the definitive aftermath writeup, as opposed to all the older news that stop at speculating about layoffs that had not happened yet)
Anecdotally, a bad employer turns into a good employer only after a death.
I do not have an example of the opposite, but I can echo your comment.
I was the first US employee of an Indian consulting startup. I was their engagement lead for a marquee account for the first 4 years and while I do not take all the credit, my management and I grew the account from 1 person to 250 by the time I left. What did I get in return? A 10% reduction in salary from my previous job, almost no pay hikes (there were some) for 4 years, a whole lot of "we are family" talk, and zero stock. Of course I was naive and did not have things in writing, but I still believe they owe me 3% of an 80 M exit price because that's what they verbally told me. But no, good employers turned into bad employers very quickly.
Of course there is a lot more to the story, I had my own faults, but I am not naming anyone and I am not publishing my story here. That life is over, I am not fighting that battle, this was 15-20 years back and I finally did move on and do other stuff.
But that 3% after a decade or more of (well managed) growth would have been awesome.