It's not worth it as a producer, or developer to even consider the option because of a few people wanting to play try-hard in obsolete content that isn't even balanced around that. The dungeon and quest overhauls of ARR was worth it because analytically that was a way to sell the game beyond the free trial and add new subs versus people whom just quit and never make it to level 90.

They already maintain so many skills across jobs plus separate PvP skills and you're going to consistently add more jobs every few years for the next decade. More to maintain and balance. Some people think in the now and not the future.