because love is what takes up like 99% of people's lives. most people would say that that's the only thing they live for - to find someone to love and to be loved by. all of life is a love story.
Love works in movies like Braveheart or Titanic but sometimes it is better to leeve it out like in Enemy at the gates(stalingrad)
lol, we have been looking at this in my film paper... if you believe psychoanalysis then this is one explanation. basically, when you are a baby you expeirence huge loss when you realise you and your mother are not the same being. This is intensified when you realise you can never see a complete, immediate image of yourself: it is either fragmented (by looking at say your hands), in the past - say photo, video, or it is a mirror image, a reflection. ok, so all this loss creates lack and we apparently search for another person to fill this void and make us a more complete person. meanwhile, there is a concept of suture, where you identify with someone in the movie, usually the protagonist. You sacrifice your id to gain theirs and in doing so, you gain meaning. now if you take these together, if you watch a movie with a love story it is like it is happening to you and it is filling this big void, as such it is immensly satisfying and you want another one. So, because we have lack we want a movie with love in it, and becauase there is demand, love movies will be made. Ah, i love my degree, it's SUCH BULLSHIT
honestly the last love story I saw and liked was Eternal Sunshine of the Spotless Mind, and I only liked it because it was so different. I normally HATE love stories. what crap. I hate sappy bullshit.
"The greatest thing you'll ever learn is just to love and be loved in return!" David Bowie, Nature boy