It's all about personal comfort. And what works best for the individual player, and having a flexible coach that can work with the player and teach in a way that makes sense to them.
Federer has said he couldn't hit a two hander well and it felt awkward and he gravitated towards the one hander. Djokovic started out with a one-hander but later switched to a 2 hander because the one-hander wasn't the shot for him.
Hopefully the coach understands the fundamentals of the one-hander and 2 hander and can teach both.
The coach I took lessons from played D1 and hit a 2 hander in college. He still had the ability to teach me a very sound one-hander when he realized that was the easier more natural shot for me.