Various reasons why steampunk is outlasting cyberpunk. For one thing, we know it's not even trying to predict the future, so it can't be invalidated. Building real steampunk engines is a quirk, not advancing the knowledge of the day.
Also, steampunk is a lot less serious. And depressing. Cyberpunk has a tendency to present itself as serious because it is depressing -- rather emo, as one panelist put it.
(And in retrospect, I think that cyberpunk tried too hard to be cool. Steampunk is perfectly willing to be goofy and earnest and all those wonderful things, where trying too hard doesn't do as much damage to the effect.)
A lot of it is the Edisonade. Which is interesting 'cause there were other forms of Victorian adventure. You don't see a great revival of the Ruritanian romance (although Girl Genius is featuring the return of the king, so to speak). And then there are the Victorian anarchists and their bombs. . . .
Cyberpunk reflected more social issues of the times. Anarchists would make a good analog to modern situations, but we don't see them. (Whereupon a fellow panelist said that the book to read about them was G. K. Chesterton's The Man Who Was Thursday. Which I, also, recommend.)
I think this panel was a little weak in that we were all pretty much the steampunk partisans. And the audience had at least half a dozen people dressed up steampunk style and only one arguably in cyberpunk style (and he wore goggles). Progress is made only in resisting material.