Earlier quoted context omitted.
And they're also free to, rather than leave their dream career, push for unionization instead and fight to remain inside it. Just leaving is one choice, but fighting is another.
But the company was there first. If the company sucks, than those devs could also found a better company instead of trying to change the bad company. So fighting, yes, but maybe for something solid.
It's legal to go find another job. It's also legal to unionize. Who are you to tell other people what to do? It's fine if you would just leave, but maybe others don't want to. Maybe they've poured their heart and soul into that company, or it's the best job around and if they leave it they'd have to move. There's plenty of reasons why people who are not you would choose to fight instead of give up and leave.
It doesn't make sense to criticize others for doing something that's perfectly acceptable just because you wouldn't do it.