You're looking at this backwards.

The only employees who make it to middle management are employees who authentically already care...

...about the company's bottom line. It doesn't matter that 90% of people realize it is a bad idea and wouldn't do it, only that 10% gets to go beyond team manager. And when you look at the distribution of employees this makes sense. As to why? Well that's an individual thing. Maybe naivety and really believing trickle down and they'll be protected for helping the company. Maybe greed and ambition and they realize this is what they have to do to move upward. Maybe some level of sociopathy or narcissism where the desire for power alone is enough to get them going.

And they really get nothing. During layoffs most people don't realize, but middle managers are on the chopping block by default. Less slaves means you need less whip masters. There's no loyalty, benefit or protection as a middle management, all their job is to be disposable villains who take them blame so execs can keep collecting their bonuses with employee moral untouched.

So yeah, makes perfect sense. If there's enough evidence that employees could sue the company, all they have to do is act "appalled" at the actions of "a rogue manager" and then "promptly discipline" them by firing them. While they get other mid-mgmt to keep trying to bust the union through other methods until something sticks.