"Don't get me wrong, I think many teachers are great and do a good job. My son's teacher is good at her job, enthusiastic and doesn't moan about it constantly. Actually, most of the teachers at his school seem good. But, I do hear a LOT of moaning from teachers (especially on Mumsnet)."
With the greatest respect, you have no IDEA whether your son's teacher moans about her job when she's not actually talking to you. I suspect lots of the teachers here on MN present to the parents/children in their schools as cheery and upbeat. It's called being professional.
"It's a good salary, child friendly holidays, and a secure job."
It's not a good salary - not if you live and work in the very expensive South, anyway.
"Most other professions don't moan as much and we all work hard."
That's quite the sweeping statement. "Most" other professions? We "all" work hard? Can you back that up?
"You know the salary, you know the workload involved. If you don't want that, don't join up or leave if already in it."
Be careful what you wish for.
"I don't care if all the moany teachers leave. We'll get a new set of more enthusiastic ones fresh from uni and excited to start in the profession."
As Noble has pointed out - the sad reality is that that is not happening and a horrifying proportion of new recruits leave in the first few years.
"I'm so sick of the glorification of teachers ("they are all amazing, I couldn't do their job, they are incredible.. blah blah blah", the moaning of teachers, and their need for constant praise and recognition."
You're nice aren't you? How many teachers do you actually KNOW in real life, who have a need for "constant praise and recognition?" And please bear in mind that those you perceive doing that her on the internet are probably just trying to defend themselves against the constant criticism and abuse we have always seen on MN, made worse by the pandemic.
"Just leave or get on with it like the rest of us."
Yep, as the thread title indicates, that is exactly what is happening. Don't forget to pop back in a year or two when your DC haven't got maths/science teachers and are in danger of duffing their GCSEs.