The reason guildleve take center stage is prob the lore behind it. Watch the intro. The games story and lore are not fleshed out yet. FF games have stuff take center stage for a reason. There might be more to the guildleve then we know yet as it isn't in game yet.

Also leve are not really quests. Its more like a Mercenary style job or a work order. (dom/dow are the mercs, doh/dol are the work orders) They are glorified fields of valor from ffxi. And ppl love doing those that they even took off the 1hr wait from doing them. It was suppose to give you a reason to go out and kill mobs, or craft.

Maybe get rid of the limitations and switch them so you get the sp but rewards every "reset" or every hour. This is what they did in ffxi. PPl slowly started to hate grinding for sake of grinding. Having an objective helps. Levequests just give you an objective.