Writing good het romance and good gay romance are two overlapping skill sets, IMO. There's a lot of common ground - more so than otherwise. But especially since people don't write about relationships in a vacuum, there's social context and how that affects the relationship dynamic, for starters. Writing a love story between a man and a woman set in, say, England in the 1800s is going to be slightly different than writing a love story between two men in that time period.

And then there's the mechanics of sex, which might come into play in a romantic fic. Lots of potential for hilarious mistakes, especially for authors who don't do their research.