I don't know which Reddit thread you're reading (there are many I'm sure) but the one in r/Aviation seems to have a favourite theory that there was a credible threat of someone with MANPADS, which are shoulder-launched surface-to-air missiles and not some sort of sanitary product.

Apparently they have a ceiling of 18,000ft which is exactly the limit of the restriction in El Paso. Aircraft are allowed fly over if they go above that