Do specialists and doctors share information?

Why don't doctors share information?
I have a neurologist, cardiologist, electrophysiologist, gastroenterologist, rhythem management, oncologist, plus
a dozen other doctors I see.
I send messages about issues and results on my chart and ask
questions for clarification. Most of the time they go unanswered.
I do the best I can to guide the path that makes sense for me.
It seems the EPIC system doctors use does not show other providers that are outside their network.