I hate to say it but from my 20+ years in the industry, this is the norm.

You are absolutely correct, but there are groups within companies that don't work like that. Finding them is the hard part :|

I think it mostly correlates with how technical PMs are.

People that were fairly technical prior to deciding to move to PM roles, those you can actually explain the context and reason with.

PMs that are more biased towards Business/Marketing are big on C Level networking etc., those are the ones that feel they are doing a good job if they try to bleed a stone with deadlines. They are adversarial like GP mentions and not someone you can reason with.

It is more common than not, but it is still best to avoid such places.

I'm a manager and when I ask my engineers for an estimate, I always, always increase it for my own purposes.

Indeed, management is very much about shielding the team, and getting rid of roadblocks.

These are the kind of managers I will go the extra mile for. Got my back I got your back and make sure you shine.