At the end of the day, the appeal of the one-sided love trope is the hope it represents, right? We read it because we want to believe that patience, devotion, and seeing someone truly can eventually be reciprocated.
It's the fantasy of being so compelling in your love that the other person can't help but finally see it. In reality, it doesn't often work that way, but in stories, we get to live in a world where love is a force powerful enough to bridge any gap of indifference. That's a powerful kind of escapism.