At first this was mostly mountain men and shifters trapped in a cabin with a scared chick trapped by a storm. But it grew to encompass more scenarios.

1. Trapped in a locale, just the 2 of them, by weather or other forces.
2. The couple who doesn’t really know each other sent on a mission undercover. This usually puts them in situations where they have to sleep in the same bed and do things real couples would do.
3. The couldn’t escape their situation if they really wanted to. Maybe she is writing an article about an eccentric recluse. His conditions are that she has to live on property and not leave until the project is done.
4. She is trapped on an alien planet and has no choice to be with him. (Probably because he kidnapped her or there are no other safe aliens around). I guess you could swap out alien planet for a mafia compound.
5. That probably doesn’t cover it all, but you get the gist.