You make a fair point, but I would like to point out that EF has successfully had industry professionals as the GoH in the past, like Mr. Jim Martin, and the puppeteers from Mongrels.
The point is not that they are professionals. The point is that you can't invite a professional musician as a guest, and then expect them to perform for free, because you made them the "GoH"
Just like we can't invite a baker and expcect free cake for everyone. Sure, you can invite him to honour his work, and if he's passionate, maybe he'll do some panels about making cake and the future of bakery in a digitized society. And if you're a fan, maybe he'll sign your cookies! But the thing you won't get is free cake, cause he's a baker, and his work ain't free.
(Unless of course, for some rason, he's got some personal motivation to support the con, then it's basically a gift. But definitely not something you can expect or even ask for.)
If I call Sony Music Live (the booking agency they're under) and ask them if their artists will play at our event for free, they will laugh at me and hang up.