Why are schools so different?

Having worked as a supply teaching assistant in various primary schools, I’ve noticed how vastly different the learning environments can be, not just for the children, but also for the staff. Some schools feel structured and/BUT nurturing, even calm, while others seem rigid, high-pressure, and almost neurotic. I’ve worked in schools that balance the core and non-core subjects, while others have next to none beyond core subjects like maths and English.

Why these stark contrasts in learning experiences across different schools?

This is almost a rhetorical question, from an observer's perspective at the ground level (contact in the classroom and immediate staff). Just wondering what gets lost in translation between the teachers actually teaching the children, and the powers that be that set the ways of the land.

I've worked for full terms consistently in schools in privileged and under-priviledged areas, with SEND needs across everywhere, around London- so not just a couple of days' impressions.