No, we have space for LB on ps4. There are many reasons people don't.

-don't know how, new.
-used to saving it for healer lb, or caster lb in dungeons
-usually doesn't play the job often, so unused to using LB at that time
-doesn't think it's necessary as melee, usually in dungeons (doesn't always speed things up that much)
-may not be useful at all (shinryu in particular, he has so much hp melee LB is less effective)