Really interesting article from Heather Massey here: Why Has Paranormal Romance Taken Off, but Not Steampunk Romance?
Personally, I think the problems come down to:
A) People on the covers of steampunk novels have an embarrassing tendency to look like LARPers. I don’t know why this is, particularly as there are far more vampire LARPs than steampunk LARPs out there, but it’s so.
B) I realise I am being a giant howling hypocrite for saying this because I have yet to write a book that doesn’t try to inhabit several genres at once, but steampunk tends to branch off unexpectedly into other genres, and it’s entirely reasonable for people to not want Unexpected! Other! Genre! in their romance. I mean, people keep recommending Meljean Brooks’ books to me and I’m sure I’d love them if it wasn’t that the first one has zombies in, and zombies are one of my ‘Nope. Don’t want to read this’ hard limits, along with heroines who whine about their weight all the time and clichéfied descriptions of Mystic Fantasy Not-Quite-China.
I was going to say that adventures with clockwork and airships are less familiar than adventures with vampires and werewolves, and therefore require more effort and more ‘what’s going on here, then?’ anxiety from the reader, but I’ve read enough paranormals with a glossary at the front that I don’t think that holds true. In fact, one of the things that seems to make a paranormal series really stick with readers is worldbuilding.
Anyway! Go read Heather Massey’s article, it’s well worth it.