Why does greater magnitude mean less bright?
See above few answers: absolute magnitude is related to luminosity; apparent magnitude is related to apparent brightness. The reason greater magnitude means less bright is just a convention. The specific form of the magnitude equation is related roughly to human eye response- a magnitude 6 star seems six times as dim as a magnitude 1 star (or, is in the “6th dimmest class”) although in fact a magnitude 6 star truly has 100 times less apparent brightness than a magnitude 1 star.
