Romance is a genre, not a requirement. Treat it like one.

To understand the allure, you must first understand the psychology of reactance. In 1966, psychologist Jack Brehm theorized that when humans feel a freedom is being taken away, they experience a motivational arousal (reactance) to get that freedom back. In short:

Storylines often fall into specific "sub-tropes" based on what exactly is keeping the lovers apart: