Bit late to this but agree it might be related to density of private schools in the area.
We visited the local catholic primary and liked it, however discounted it due to 'skirts only' (despite at the time having only a boy). Then visited all the other local primary schools and found, to our horror, that every single one of them had the same policy (no, hang on - one state community school stipulated that on exceptionally cold days in winter girls were allowed trousers, but only if the head had given express permission beforehand). Short of moving out of the area, we'd have to go with a 'skirts only' school.
And yes, there are huge numbers of private schools in the area.
The one school that has changed its policy since, now allowing trousers for girls, is an infant school that takes children mainly from a not-well-to-do estate and is avoided by aspiring middle class families.