Action heroes tend to be romantically active. Even if they don't have sex onscreen they are probably going to end the film in a relationship with the female lead and if their original lover dies at the beginning of the film they'll probably pick up a new one by the end.
When the lead character is female though this seems less common. An action heroine protagonist is probably not going to end the story riding into the sunset with the male lead. If there even is
a male love interest he will probably end up dying pretty early on and unlike the action hero's equally disposable wife he won't be replaced. Additionally it is very possible that the heroine's (ex)love interest is evil and will end up dead so no relationship there.
Notably, an action herione is less likely to be trying to save a boyfriend or husband. More often they will be driven to rescue or protect a child.
See also Final Girl
- Ellen Ripley does have sex in the Alien films but none of the men she sleeps with (a) survive or (b) form much of a connection with her. When it comes to saving a character she is far more invested in saving Newt.
- Sarah Connor's love interest dies two thirds of the way through The Terminator and she doesn't have a love interest at all in the sequel.
- Evelyn Salt's husband dies pretty quickly.