While I would be all for using gear from other classes, I've seen far too many players who don't know what a job crystal is or how to acquire it in post-30 dungeons and seen far too many tanks who literally do not know that they are meant to tank. I've been in runs where the tank would grab one out of four or five enemies and literally just attempt to DPS that single target down without once touching the others that were attacking the party.

It may sound like a very bad reason, but after playing since 2.0 and seeing players brand new to MMOs, I've come to realize that there are many players who literally don''t know what they're supposed to be doing. Heck, I used to be one of them. I started as Archer and I knew, without a doubt, that I needed to equip Strength gear despite being told otherwise. God forbid these new players see tanks wearing mage gear and don't realize that it's just glamoured.