Obsession is a hit because it shows how "regular" men's romantic fantasies are unhealthy and often fantastical, and how even well intentioned actions can cause devastating long lasting harm to the women they pursue.
Obsession was extremely popular because it fufills the female notion that every lonely mid guy is secretly a rapist monster and deserves to be miserable and alone.
It would have been a nothing movie if the genders were swapped.
Conversely if the rapist monster had been 6'3, extremely attractive, and a millionare, it would have also been a wild hit with women.