Earlier quoted context omitted.
Depends on the country, I guess. In Europe, it would definitely not be the norm and I would definitely call previous employers if it was several 2 year stints.
Europe is not a monolith. Lots of short stints is not unusual in London.
I am not saying any of these don't have valid answers. What I am saying is that we would prefer juniors that are commited and do the hard work when the work gets hard. And, at least where I work now, this gets recognized, and they become seniors in time.