The motivation's usually not just coldly calculated and personal outcome focused. The urge to even the playing field by any means necessary is a strong human instinct. I always remember an old experiment where two monkeys are happy to do simple "work" tasks in exchange for treats. Until they start giving one of them better rewards in front of the other's face, then the underpaid one starts losing its shit, throwing stuff at the experimenter and refusing the task entirely. And I definitely see that mirrored in a lot of actual people, the message of "don't fuck me around" is more important than the money sometimes.

[Edit - Gah hit save early]

For places like antiwork tearing down those at the top of exploitative corporate culture is just as important as improving their own lot. They want to see Bill Gates drag his old ass to the bus and get his own groceries, they want to see Bezos try to decide if he can afford to get that weird lump checked at the doctor's this month. It's like crabs in a bucket mentality, but done kinda right, they're reaching past the crab slightly above them and trying to cut the hand that keeps shoving them all in a bucket.