Yeah, that is pretty much my experience. I asked for direct submissions from the public, but I didn't get that many. I specifically didn't get submissions on topics where I directly asked for them. A lot panels where made up by me (or angriest or by group effort, not because I think that is the best idea, but because I simply didn't get enough suggestions.

And people who haven't done it don't know how to create a good panel instinctively. Often a little rephrasing or restructuring of a panel can improve it significantly.