There's only so much SE can do to encourage more people to level up Paladins, Warriors, White Mages and Scholars. The rest is up to the community. Adding more tanking/healing jobs would do very little (at best) to alleviate long queue times for DD classes.

So, yes, the root of the problem is the players. Hell, I would tank or heal (I personally love the play style of the Marauder & when out in the field I'll toss a Physick out on others when I'm a Black Mage) but I'm reluctant due to the animosity that the community has towards each other. Nobody wants to deal with a tank or healer that's new. And a tank & healer can read all the guides and watch all the videos available but it doesn't compare to first-hand experience, which is how one truly learns.