Ran Omega V3 with a friend, he was on Sam. Everything looks under control, Lb3 is up, so he uses it. Minutes later someone messes up a mechanic and we wipe. The healers both immediately start giving my friend shit about why he used Lb and that he should have saved it for the healers.
Next pull Lb3 fills up again, noone uses it, we clear the fight without using it. Healers start going on about what a waste it is and why no dps would use the Lb3.

So yeah, I believe that's why a lot of people rather don't use it.