Well, there can be more perspectives to this

  1. At this point, there was mutual interest. If there was none at all, you’d never had went out together. There was a point were you both were interested.
  2. There’s always the chance the someone felt something more intense than the other. So, for someone it feels like it’s worth trying in a way that’s blind to the fact that the other doesn’t feel it.
  3. Things worth having need work, they don’t fall from the sky. At some point, beyond initial mutual interest, work is needed. Of course.