I'm not sure I fully get the question.

The landscape of romance novels might be getting different now, but from what I used to see, a lot of the older romance novels feature mainly standard heterosexual romance. So I'm not sure why there would be a term that's overwhelmingly used as there generally wouldn't be such a term?

But that’s my question: why wouldn’t there be?

Can you think of one?

I’m not a woman and I don’t consume romance/erotica so no. I’m only aware of how big romance is because I’m a writer, and it’s no secret romance authors far and away make the most money.