Often DPS don't use the LB on-demand because it's not a safe time in the fight to do so. LB roots you in place for a rather long time and can very often lead to you dying if used at the wrong moment. I've had it happen to me quite often when I've mistimed the safe period in a fight or caved into the demands of tanks/healers that don't know what they're saying.

Also a DPS in the middle of a burst is not going to waste the burst using LB as soon as it comes up. If the LB meter ticks over just after I've used Riddle of Fire, for example, imma wait till my fire goes out before using the LB.
Both of these are big contributors to my "yes yes, I know to LB, shut up and stop hassling me about it" moments.