It's obviously true that being banned from contributing to an important project can be saddening and in rare occasions harm your career, but it happens very rarely.
OTOH losing your job can be way more serious consequences and happens way more often, even without any blame on the employee (e.g. a company shutdown)
And on top of that, a project BDFL cannot order inactive contributors to do some work under threat of banning them.
It's obviously true that being banned from contributing to an important project can be saddening and in rare occasions harm your career, but it happens very rarely.
OTOH losing your job can be way more serious consequences and happens way more often, even without any blame on the employee (e.g. a company shutdown)
And on top of that, a project BDFL cannot order inactive contributors to do some work under threat of banning them.