I was a teacher and am one of the 'oldies' who left the profession.
Reasons? Too much red tape- I taught before the NC was introduced and didn't like being told what to teach. (English was my subject.) I also disliked the dumbing down of the subject compared to how it was when I entered the profession in the 70s.
Hours of work- my teaching career was split between state and independent schools. I can quite honestly say that teaching in the private sector was MUCH more demanding- had to teach lots of activities after a day's teaching. (I taught in a boarding school.) You really had to give your life to the school, compared to a state school.
IME the hours of work depend a lot on your subject- the English literature syllabus can change annually- choice of texts for exams at GCSE and A level- and this involves a huge amount of prep if you are not familiar with the texts. Similarly marking an A level essay is more time consuming than marking some maths answers.
Pay? It's a lot better than it was. If an experienced teacher can earn almost £40K that's not bad, taking into account the holidays- which are generous. The average UK salary is around £27K - just to compare. Anyone going into snr management in teaching can earn a lot more.
My DH is not a teacher and the graduates in his organisation ( huge multi national) earn around the same as teachers- and many of them have masters degrees- unless they climb the management ladder over time. They also have just 25 days holiday annually and most work- like DH- from 8.30 - 6.30 every day. He also loses time at weekends if he has to travel overseas or in the UK for Monday meetings- none of which is paid for - it's just 'the job'.
I suspect there aren't that many teacher who put in more than 2 hrs a day, every day, after lessons are over.