Carts just don't wick fast enough to keep up with the juice demands of LR's. Even if it's full, if it's not wicking fast enough it won't matter. They need more juice, because they get hotter and vaporize juice faster.
I've heard of a couple people who use carts with various mods with LR's. But it's very uncommon. I don't know how they do it, because I have never found a cart that could keep up.
With LR's, unless you are one of those rare people with magical powers to make carts basically dump out juice, you gotta drip. Tastes better anyway, ha ha.