It's because people tend to start threads when they have something negative to say.
For example, if you spend too much time on MN you'd end up convinced that texting a colleague is always an affair, that relationships aren't equitable, and that most men are manchildren who refuse to pull their weight.
If you spent time reading some teaching forums the you'd think all schools are terrible,any constructive criticism on a lesson is workplace bullying and senior leadership are always wankers.
Same for school threads here, nobody posts about the normal days, the fact their child likes their teacher, that they're quite happy. The people who post are the ones who have a genuine concern and are seeking genuine, helpful advice to resolve it, or they're the ones who are raging, fuming and incandescent with rage over the fact their child was given a detention for repeatedly ignoring instructions.
They are very defensive and would never, ever give up their extended holidays. They live in a bit of a bubble, a lot of them are kind of institutionalised. They start their lives as children in school, they go to Uni, then back to school. They tend to mostly socialise with other teachers so it's the only world they know.
It's this sort of thing that tends to get backs up.
Why would people want to work more than the 195 days they're contracted to plus some preparation time on top of that?
I'd gladly shorten some of the holidays if workload was more manageable during term time AND my pay was increased to cover the additional days working.
Of course, pointing that out then gets branded defensive so it's no win.