It's the unrealised promise or illusion, at least for me. I was a huge fan of him, mostly due to SpaceX, and still follow bigger events or announcements regarding his company. But he really disappointed me with his personal opinions and management practices, multiple times, even before Twitter debacle.

On the other hand I don't have any hopes for Bezos or some Comcast or BP billionaires as an example, so they don't disappoint me much :)