I think its more of a "people don't know when/where to use it" kind of thing, its easy to burn Raw Destruction/Cometeor but at least you usually see some kind of effect out of it (unless you miss Cometeor, lol), tank/healer LB... its easy to waste and get no effect out of it.

Its really just due to the nature of the jobs imo, for tanks its like using defensive CDs/push back, some people just really don't know "when". I'm not sure what could be done, honestly.
Plus from a PvE PoV its pretty much beat into the average tanks' head to NEVER use LB. Arguably same with healers.

I feel like the most you can do is just tell people- I've had games where no one used tank LB despite us having 3 other tanks besides myself in the party until I told them "use it when we push or get rushed, don't worry about anything else". I feel like that's the most you're gonna get without a properly co-ordinated group.