Boy Meets Girl, in a petri dish under a microscope.

Is it typical in love stories to not bother explaining how the protagonists actually fall in love? as in, what causes the initial attraction that motivates them to overcome the various obstacles that then crop up to keep them apart, instead of shrugging and moving on to the next possible match? (Perhaps they do explain this and I miss it somehow?) This would make writing love stories exponentially easier; sort of like the difference between space opera and Hard Sci-Fi (where you have to explain how stuff works as if it really might).