You're assuming your line manager has the power and/or budget to hire more staff. This is likely not the case for the vast majority of salaried employees.
Then it’s the managers job to manage expectations in terms of what her team can produce. The occasional push should be acceptable, but sustained expectation of unrewarded overtime with implications for burnout shouldn’t be acceptable.
Another point, we all get things are limited, but when the hierarchy/management simply orders shit to be done from afar, without respect, understanding, proper knowledge about the situation, suddenly everybody is underperforming. Take the same group with a good leader then they will do twice more twice fast twice happy.
That’s not my problem? I’m not going to give away my valuable time for free because other people cannot run a company.
What?! Of course nobody thinks that, but they have the power to influence the people that do have the power to get more budget, that is part or their job!
> You're assuming your line manager has the power and/or budget to hire more staff