Well the one most responsible for popularizing that was the late Gary Gygax, as he was the one who originated that idea of "healers cannot use bladed weapons or mages cannot wear heavy armour that would prove too distracting to cast spells" in Dungeons and Dragons, which computer RPGs and MMOs like FFXIV are all descended from (FFXI's manual even stated that outright in it's Job descriptions for BLM specifically, that BLMs "Cannot wear heavy armour that would otherwise interfere with their ability to concentrate").
Most RPGs still use tropes and ideas Gary created for DnD like exp, levels, stats, HP/MP, character classes and yes, restrictions on those classes. And FFXIV is no different. Once again glamour ties back into that.
