The reasoning behind tying it to a job rather than gear is due to jobs sharing armor, though. If, for example, you main blm and really love the blm specific AF and you glamour it over the Evenstar stuff, it's fine when you're on blm. But switch to summoner, and the blm glamour doesn't show up so it just looks like you're wearing Evenstar. If you could tie glamours to jobs you could have different outfits for each one.