I imagine studios, and the people they employ to create products for them, share a goal - to get as many people to engage with that product as possible. For the studios there might be more of a financial incentive to that, for the creator maybe more an artistic one. Either way, the more people engage with your creation the better.
People like love. They like to see people looking for love, finding and losing love too. Most humans can relate to that. It drives a lot of human behaviour. We seem to seek out stories that reflect that. I think a big part of it is living vicariously since real-life love is often unavailable to us (either because the other person isn't interested/available or due to our tendency toward monogamous relationships).
Does it really seem strange to you that love would figure so large in our popular culture?
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The world is a big place where things happen almost every day.