Being a manager is an invisible job. When everything goes smooth then 'that's just how it's supposed to go'. When things break or get hacked the manager looks like they aren't doing enough. Meanwhile manager responsibilities cover an unreasonable amount of work and stack up fast.

Managers can be in a good place work wise and then get 1 phone call that ruins their schedule for the week. When it rains it pours because then employees call out, some employees can't get along so you have to deal with their high school drama, then someone needs a report, then there was an inventory supply or a computer/accoubt isnt working etc etc etc. At some point the manager has to say 'this isn't my company and I'm not going to put in a bunch of unpaid overtime (your salary and only get paid 40 hours a week. Anything over is you working for free instead of enjoying your personal life) to fix this'.

Just like the people they manage, managers aren't very incentivized to sign up for their own big projects that don't require their immediate attention. Managers might get a bonus for a job well done at the end of the year but is it really a bonus if they worked a bunch of unpaid overtime all year? Feels more like a partial refund to pay some of that time back.