I agree with you, but I feel like leaving is much harder in reality for most people.
Life gets in the way, you don't have the energy to apply, you're afraid of rejection, you are afraid you might end up in a worse environment, you justify it to yourself in any number of ways.
Inertia, herd mentality and self-deception are much more powerful IRL than most people online seem to think (or at least write).
Add having a family to the mix and it gets worse. Being a sole provider for a family is scary when you go job hunting, especially if you live in an environment that is very expensive (where the jobs that pay decent are located normally).
Yep, I left one project because I think I was underpaid there. I could not find another job for like 3 months. I finally found one and I was also very stressful. No it is better, at the same project and I think I make more money than I would ever be able in a project I left. But on the other hand it was very stressful for my family. Was it worth it in the end? I do not know because even if money is better and company is bigger I could damage my kids development by being angry, sad and depressed for two years.