Steampunk is a modern retro movement. It is not Verne and Wells, but modern writers writing in a Wellsian mode. Why this should have come formed around a group of writers who, perhaps not coincidentally, had in their younger days been friends with Philip Dick, is unknown.

Gibson and Sterling were actually somewhat late to the game.

For me there is no better example of that aesthetic harking back to Verne and Wells than the 1902 Georges Méliès film, Le Voyage dans la Lune.