Interesting topic - the love triangle with the bad guy and the good guy fighting over the same woman is definitely really popular. I've seen it with two women both in love with the same man, too, but rarely the other possibilities you mention.

There are some stories where I think this plot is really well-done (I'm a fan of the Gothic romance where Our Heroine thinks she should choose the Good Guy but really she's attracted to the Bad Guy but it turns out the Good Guy is actually a villain), but I agree it's disappointing that there aren't more varieties of story out there.

It's important to recognize tropes, because they say something about society and expectations.