Heh.

It's always been a consistency issue for the series, how they justify this bit of fanservice. Supposedly the strikers require skin contact, so they can't wear anything below mid-thigh while using them, and they have to be ready to deploy on a moment's notice so even pants they could just drop are a problem.

Except that we've seen some get away with tights (Eila) or long stockings (Lynne), so that's not necessarily true.

My No-Prize Headcanon: It was true of the pre-Miyafuji-engine strikers used in WW1. The new designs are more efficient and don't require quite as much contact, and are faster to start and launch so the short reaction times aren't quite as much of an issue. By this point it's just a Thing that witches Do, in order to differentiate themselves from normies. With all the recent proclamations on the Role of Witches in Society, I think we may see some changes in fashion soon... whether towards regular pants, or towards more general adoption of 'witch-style', who knows?