One thing I have to point out is that a lot of people seem to expect of melee DPS to LB3 the second the bar fills up. Doing that is a good way to get yourself killed, because LB3 has both a sizable casting time, a short range and a long animation lock. A lot of DPS have to spend some time waiting for the right moment that accomodates this.

Additionally, a lot of players are still inexperienced and practising with or progressing through content. Because of this, saving LB3 for the healers often becomes more important. I have had at least two dozen wipes that could have been avoided with a Healer LB3, but instead a DPS decided to use it prematurely.

Unfortunately, a lot of players don't seem to recognise either of these things.