Nothing more need to said. And of course we do develop theories about what is funny, what is sexy. Those are the things you need, I think. Here are the things that are working against you when you're doing a romantic comedy. It's right up front because you know that they're going to end up together, and technically speaking, you're dead in the water before you start.
Predictability is one problem.
The second is what we traditionally call soft conflict which is precisely because it's motored by what's usually the B-story and kind of inner track of emotional stuff. It's perceived as being soft. Exceptions like Romancing the Stone, which is an adventure romantic comedy. It's really hard to find one that works. For example, Cats and Dogs didn't make a huge amount of money, but for what it cost, it was a total success.