I'm guilty of forgetting to use the caster limit break on trash most of the time. If I'm on a melee DD I use it on bosses, which is kind of funny considering SMN is my main.

I think, as an explanation but not an excuse, I tend to focus a lot on my AoE abilities and build-up and forget to look for a good time to use the LB. I would expect BLM is largely the same, they lose their stacks/Enochian and Flare build-up and might be focused on executing that instead.

I will say that I never take it personally or think it's rude if someone just chats "LB." If you're the tank or healer and remind me, I'll feel dumb for forgetting again, but I will do it. I've noticed saying the same for melee on bosses (and ranged/casters when no melee are present because they aren't used to doing it) often results in it getting used. Some people just need a reminder and it doesn't hurt.