They used to let you do a pseudo sub-job thing where you had to play a class up to 30 to unlock what are now certain role abilities and to get a job stone that combined aspects of two classes (iirc, for example, to get warrior you had to play gladiator and pugilist to 30 or something, look this isn't important). I think the player base at large decided it was hogwash and pushed back against the devs hard eventually to get it changed. So what I'm saying is that it isn't that they didn't try, but a number of factors led to them scrapping this idea.