You forgot the second part :-D

I think the answer is pretty simple: it sounds good, and it's hard to challenge. It's essentially a promise that they will invent a black box with magic inside. Since nobody can see inside the black box, it's hard to argue that there isn't actually magic in it.

The long-term problem, of course, is that there aren't that many actual magicians in the world. Most of the people who bill themselves as magicians are either people who just think they're magicians, or people who know they aren't but don't mind lying about it.