The reality is that every school is different, though, and every teacher becomes used to the environment they are in.
I work in a top private school in London where we're paid over £60k as a basic classroom teacher salary and have 15 weeks' of holiday a year. I have a very easy life and will do a bit of work at the weekends/in the evenings at crunch points of the year, but the reality is, most days I work 8-5 and I enjoy my job. The kids are well behaved and like learning. I have a decent leadership team who leave me alone to do my job. I have great colleagues. I can't complain.
I know plenty of teachers who work in inner city London comps who work 12 hour days, all weekend, and deal with horrific behaviour incidents every day. They are surrounded by colleagues for whom that is the norm and they have convinced each other that is just what teaching is. Many of them take a sort of absurd pride in being martyrs to the cause, and won't leave because they 'can't abandon the kids.'
It's these kinds of teachers - the ones who wear their suffering like a badge of honour and accuse those of us who have left state for private as traitors - who perpetuate workload problems, because they are willing to put in 12-14 hour days, and they make this the norm. They then get promoted and continue that culture within their schools.
It does have to stop but the OP is right in saying that teachers are part of the problem. There does come a point where you have to say no. In my first school, the whole English department banded together and went on a marking strike until we were given an extra member of staff so we could actually have a manageable workload. Collective action works. But in too many schools there is a lack of cohesion and camaraderie amongst staff - there is a huge amount of game playing, back stabbing and pettiness in staff rooms, as many teachers have never mentally left the classroom and a lot of them are trying to climb the greasy pole to earn more money - so it's hard to get people to put their heads above the parapet and say no when no needs to be said.
To put it bluntly, there are many people who become teachers because they enjoy having power over other people. Not because they love children, not because they love learning, and certainly not because they have a passion for their subject. I've worked with many teachers over the years who were sadistic bullies, and who were thick as two short planks to boot. No prizes for guessing that they were often promoted to SLT very rapidly, and set about turning their schools into mini fiefdoms. Many state schools are populated with these types, as well as young and impressionable NQTs with mediocre poly degrees and poor GCSEs and A Levels, who don't have much subject knowledge and for whom teaching is bloody hard work because they don't have the mental, intellectual or emotional agility to cope with the pressures. These are the types who do have to work all the hours God sends not because they want to sacrifice themselves for the greater good, but because it genuinely takes them forever to plan and mark lessons. So many of our schools - particularly in areas where school intakes are problematic - are staffed by a mixture of sadists, narcissists, martyrs, and well meaning incompetents. It's no wonder schools are in crisis.
The reality is that there is such a major issue with staffing now, that if teachers did collectively get together in schools and start instigating action short of a strike (i.e. refusing to work beyond their contracted hours) their leadership teams would be forced to sit up and listen. But it's finding the will to collectively get together - when teaching is exhausting, there's always exams or reports or some other crunch point to get through, and when you've got people who are too scared to do anything for fear of losing their job (and god knows why, because most of them don't have a job worth having), it's not as easy as the movies make it out to be. Plus we have to remember that many of us (myself included) genuinely love our students, and the thought of hurting them through taking action often stops us from putting our own needs first.
It's a tough one really. It's a complex issue and not easily solved. But I don't agree with the narrative that teachers are overworked victims - some are, but many aren't, and in the right school, teaching is a joy and the best job in the world.