>I'm sure that's part of it. (Similarly, the people who have to pay
>for costume designs in anime must thank their stars every day that
>they live in a country where public school uniforms are a thing,
>although that said, the K-On! girls do have a respectable range
>of civvies over the course of the show.)

Tangentially, it's a running joke around here that over in To Aru Kagaku no Railgun, most of the cast sank their entire budget into superpowers (some more effectively than others), while Ruiko Saten sank all of -hers- into the costume department. And thus is the only one to ever be a) seen in more than one outfit per episode, and b) seen in something other than her school uniform.