For me it's role playing. I wouldn't enjoy having one character be a master of every job. I'm playing through as half of the jobs now, and will play through as the other half in the future.I don't see the point in creating a new character? I mean that as an honest question. What are the benefits?
If it's because some of your skills are lacking point, well you can still upgrade them whenever you gain a level (except if you're already at level 200 of course)?
You get massively overpowered just from taking three jobs, let alone six or twelve. I want to experience everything the game had to offer while still keeping it somewhat of a challenge. I'm not here to get another notch in the belt or think "whelp check that game off the list".