Mostly because it is still innovated upon. Async payments (offline receival) and trampoline payments are in the pipeline, allowing true self-custodial wallets on the smartphone.

That aside, I only use lightning with my Bitcoin-friends to settle stuff for fun. I live in a city of 300k people, and there are 3 restaurants that accept Lightning payments. Right now it is in its infancy, but I see Lightning as the only solution to actually enable web micro-payments (which failed as a standard because no credit card can provide .10 to .20 cent payments due to high fees)