FIM’s target demographic is little girls and their parents. So to that effect things like sex, sexuality and, bodily functions being topics considered inappropriate for this audience are not really taken into much account, despite being strongly implied. So it’s really up to the artist or author to imagine how these things would affect pony clothing practices. In the show ponies go around without clothing most of the time and, don’t really care. Cloths seem to be largly a matter of choice, preferance, uniform, or utility. I would consider military to focus on uniformity, utility, and protection myself. Ultimatly it’s up to creater of the work. I support the creator’s work, whatever they go with.