The game's GUI also actually states your current class/Job's abbreviation above your EXP bar in the game by default anyway, so there is really no excuse to get the official abbreviations wrong, and some of the abbreviations originated for the same Jobs back in FFXI (like White Mage=WHM), so some at least should be familiar to many players. I think some people just get used to calling them a certain way and it's a tough habit to break.