Post2:

Now, if you're going to keep classes around, it would make sense that each class is the root for 2-3 different jobs (maybe more). If THM, at 30, branched out into 5 different flavors of caster, each one unique from the other except for the base THM skills, then I'd say classes make sense because the first 30 levels of a class would effectively be the first 30 points on a "talent tree" of sorts that the player will later branch off on.

But most classes become one job, and most classes are not in any way better off for NOT becoming said job, ergo I can see why they'd want to stop adding classes at this point.