Maybe because they center too much on them, giving the impression that there's nothing else going on in the world.

Exactly. And it's not relationships (or love, or emotions generally) I'm opposed to, but what interests me is a *connection* of characters, a mix of characterisation and plot that goes beyond teh pretty physical attraction and what often appears like a mere shuffling of cards by the script writers. Connection, a kind of mutual need, a *reason* why two characters would be drawn to each other: that's the emotional appeal, no matter whether it's friendship or love.