With all of the gear (including relic weapon) and skill required to master a particular job in FFXIV very few people can be every class or job. I have all of mine at 50 but I typically stick to warrior and white mage because those are the jobs I have the best gear for, and most experience playing.

As the game ages this will become even more true. Fewer people will have everything at endgame potential when the time involved to get all the adequate gear and experience is multiplied several times.