Second, it would be absurd to account for extra income to say they make what you're saying. That's like saying a cashier at walmart works three jobs to make an average of 70k a year, so cashiers at walmart commonly make 70k a year.
Except it's extra income that they make by being a police officer. A business that hires an off-duty police officer for security isn't hiring them because they're a big burly-looking dude; they're being hired because they are a police officer. An off-duty officer will typically wear their police uniform while working "off duty", and can take actions which an ordinary civilian could not (like conducting arrests).
It's not what I say they make, it's what the public records say they make. You can go look yourself.
For example, from my first link, Sergeant Stuart Eugene Barnes made $125,380.76 in salary and $172,330.17 in overtime. I think it fair to say that's compensation from their job as a police officer.
https://oaklandnorth.net/2021/04/28/oakland-police-overtime-...
Kind of makes sense though, most officers start there then move to a safer place once they get enough experience. Remember seeing billboards advertising $80k starting salary 10+ years ago while driving through town.
As for your second part, I guess it would seem unlikely for some positions, but I know a doctor who made like 3x his base salary each year through all sorts of absolutely legal, ethical, and hospital-sanctioned means. Taking every single weekend he could on call (even offering to "relieve" other doctors who had been assigned that weekend) for example allowed him to make much more than you would ever think possible.
An administration that squashes all overtime faces extreme wrath. They can be cutting employees' take home in half. I and plenty of others have seen people lose their houses or suffer other financial crumbles when the expectation of built-in pay far beyond their published salaries were cut off. You can argue that it is foolish to depend on such extra pay and I would agree. But when that significant extra has been their reality for all 10 years of their employment with the department, you can see how they would just plan it into their future finances.