Besides, I don't think it's really a fair comparison. Vampires are just one thing, one category of character or trope. Undead, bloodsucking, evil and/or tortured, just a few variations on a pretty repetitive pattern. Shows that are initially about vampires tend to need to broaden their focus in order to generate enough stories; Buffy the Vampire Slayer got to the point where the vampire slaying was a sidebar to battling demons and cyborgs and elder gods and so forth. But space opera is a far broader and more versatile genre. It can encompass just about anything -- including the occasional vampire story. So it's not as easy to get bored with.
But most "vampire shows" also feature ghosts, witches, werewolves, mummies, etcetera . . . like most space operas tend to include aliens, androids, cyborgs, mutants, and so on.
So maybe the more valid comparison is not vampires vs. space operas, but supernatural fiction vs. science fiction.
Not that there's any need to choose sides. That's my whole point.
I was raised on Star Trek and
Dark Shadows, Forbidden Planet and
The Wolf Man, Isaac Asimov and
H. P. Lovecraft.
Genre fiction is large; it contains multitudes.