For multiple reasons, but the most important one is that sticking around and making your voice heard may get you what you want. That's how change can happen, and you getting what you want. Quitting lets them get away with what they want and how are they doing things. Facing a strong employee that insists on taking his rights and imposing his will is HOW THINGS CHANGE, and you manage to get what you desire from the job.
If your lunch break gets taken away from you. Take your lunch break. Tell anyone that asks why or how, that you are taking your lunch break. If they threathen to reprimand or to fire you, let them. If someone quits and you are asked to take on additional responsabilities at no extra compensation, say you will not do that. If you are told you can't take pre-approved time off, take it anyway. Tell them you won't be in tomorrow or whatever it is, and just say you won't be there. If they start raving, let them rave. Ignore, do your thing. If you come to work and your job is not there for you, you get unemployment.
IMPORTANT: Do not argue WHY, or HOW, let them get faced with the stone wall of a “No” or “I refuse”. Those are extremely strong when the other person has nothing to grasp on to. They can and will argue themselves into whatever narrative is in their head, and even getting the 'fight' is enough to stroke their egos or whatever the movie is in their heads. Again, do not explain why, or how or if when faced with a person that you know you cannot communicate with. Say what will happen in the immediate and let them deal with it.
If it's a milder situation with a person you know you have some leeway with and can communicate at least somewhat, you can show empathy and compassion and explain your reasoning but in the end, do not budge.
Storytime. I once worked at a place where it was slowly downsizing (or people were leaving on their own accord and we were not rehiring), and tiny tasks kept getting added to everyone's load. Initially it was a 'might as well, i'm already here', but soon became things you needed to coming more for, or taking time out of your day that wasn't originally busy with your existing responsabilities. From the get go i was 'an asshole' and said no. I worked tech support internally and i was overwatching things going to plan on a regular, and i knew all the devices and workflows. When i got tasked to actually do the thing, i said “No, i'll be there, watching as the thing is NOT getting done, even if i have the knowledge to do it, as it's not part of my job”.
Again, i made some enemies there, but six months down the line, i was the only one with a light workload while others were pulling in all-day-workloads (not because of me), even if people on both sides were miffed at me. Spoiler, some people WILL hate you or dislike you even if you don't intend to and you're at your best with them, you have zero control over that, so might as well be something you actually intend and benefit from. But i was not fired, and i was not going home stressed or tired, and was getting paid the same as everyone else.