Because they have nothing to lose. If they get fired, off to unemployment where they will make just as much money, get their housing paid for, ebt card, child care or more money for each kid, etc etc. so why not go for major pay raises where it is actually worth more money for them to have a job.
If we got rid of these entitlement programs more people would be fighting for these entry level jobs....and respect actually having a job.
Pilots have a lot more to lose. We, well most of us, have our eye on a future at captain pay, major or legacy airlines and a future where you have the chance to make several hundred thousand dollars a year.