Why does everyone blame the tank?

[NintenPyjak64]

My lv50 friend ran with a 48 pugilist the other day When my friend asked him why he easnt monk yet, the guy responded "how do I do that?"

Is there any reason to not change jobs once you hit 30?

There is no reason. There's no reason to not do your class quests which guide you to your job quest anyways. If you're above 30 and don't have your job yet, then you are being lazy, simple as that