No, it's not that. It's just that straight couples are the default, much like white male is the default in America. When you're the default you don't have a lot of opportunities to relate to the not default. Media provides ample opportunities for minority ethnicity members to relate to generic white people, but not for white people to relate to minorities. Women are expected to relate to male protagonists no problem even where there are massive differences in how the genders think and operate, but men are not expected to relate to female protagonists with nearly as much regularity. And I think it's the same thing with sexuality.
You can't catch the gay and I don't think anybody actually thinks that. But when you're not used to seeing the beauty in homosexual romances because you don't have enough experience in the matter then it's off putting. It's unusual and even in some places described as wrong, so people are averse to normalizing it. It's not about worrying that people will turn gay, it's about having to learn to accept that gay people are normal.