Why do some people expect romance when the main characters are a boy and a girl?

I'm in the process of outlining a story where the main characters consist of 2 girls and 1 boy. And usually with books like these, eventually, the boy might switch between the two girls in some sort of a "romance" known as the love triangle. I like to call it the 'bermuda' love triangle, because it's almost always disastrous. I don't want to tell you what the story is about because I don't want anyone stealing the idea, but romance isn't really needed in my plot, yet people always expect you to write a bit of romance! Why is this? Just because there's a boy and a girl doesn't mean they'll "click" like that, you know?