We just need one umbrella tag to indicate that someone isn't wearing any garments covering their bottom region (but still have underwear). We don't need to split this up into no_skirt and no_pants and then requiring the tagger to figure out whether the character normally wears a skirt or pants. And searchers to use two searches to catch all examples (or "or searches" denying the use of wildcard search or other "or" searches).
There is virtually no benefit to this at all, and any mental disconnect with using no_pants for "characters that are generally not seen wearing pants" are already handled by the skirtless and no_skirt aliases.