Why so many players with base classes when they could already have a job?

[Polares]

And they usually don't answer when I ask. Only one guy has answered before when I asked why he was a thaumaturge when he could be a blackmage, the answer was something like: "I am drunk right now. I don't want to talk about that".

Am I missing something? Are there any advantages? In the picture, 2 lancers and 1 archer, above level 30.