Teachers don't get a say when the INSET days are.
Blame it on the governors. They, along with the HT, decide when the INSET days should fall.
I know, I am a teacher and I've been a governor.
Quite often the INSET days are tagged onto a holiday because it's felt that once a parent has arranged childcare for a week, they may as well book it for a couple more days. Unfortunately, they don't always consider that sometimes parents have to beg, steal and borrow to provide childcare for that week and an extra day or two feels like a pisstake.
OTOH, parents can organise their workload around that so not book meetings, organise projects and shifts to cater for it. Whereas if you have a random INSET day in the middle of the term, you'll find there are parents who find it difficult to organise childcare for that one day/arrange the day off work.
It's a pain for someone either way.
And don't get me started on INSET days at the start of a term when the focus means that at the end of the day to have to revisit your medium and short term planning and get your head round it before the start of the new term the following day.
That's helpful. Not.