I think a lot of it has to do with the fact that he's a very prolific writer and speaker, in addition to contributing to a fairly diverse set of Computer Science fields.

I usually enjoy Lamport's speeches, and I have said before that his book Specifying Systems should be mandatory reading for nearly anyone interested in CS, due to how approachable it is, and yet how deep it goes.

It's interesting that you mentioned Dijkstra because Lamport in one interview said that the original Paxos paper (The Part-time Parliment) was written in the way it was exactly because he was inspired by Dijkstra in his famous examples such as Sleeping barber, etc.

Dijkstra was and Lamport is very good at writing clearly and distinctly. Many people with that level of raw brainpower don't make that effort, so the ones that do are easy to admire and be grateful to.