In my case, I get the impression that it's both.
Once during 2020 I got a phone call out of the blue from the technical manager. "Hey, would you like to be our new <first name of the one who used to hold that position>?". Turns out my predecessor was looking for greener pastures.
When I told some coworkers about this, their reaction was "And you said yes??"
It's been four years now. Changed to a new employer last month, but I'm doing the exact same stuff, and I enjoy it.
I think he wanted a different type of job. I, on the other hand, recently moved on to 30% greener pa$ture$, as the competition successfully poached me. Same type of job, exactly the same area of responsibility (networks and server clusters running in weird/hostile environments (no, not the Hamas installation under that hospital)), but with even more freedom and higher budget.