In my experience, when they're top tier math researchers they tend to be oblivious to the student's perspective, grasping the problem too well to give it detailed treatment. This is neither a failing of their enthusiasm nor a social tactic, but an imbalance in their abilities.

An old anecdote is the professor who was asked by a student how a certain problem is solved. The professor paused in thought for a moments, then gave the answer. The student asked again how to solve it, and the professor, again, thought for a while and gave the answer.

The student persisted: "but how is it done?" To which the professor gave a frustrated look and said, "I already solved it two different ways, what more do you want?"