Why should I attribute emotions to you?

I seem to ascribe emotions to a system -- more generally, I ascribe cognitive states, motives, and an internal mental life to a system -- when its behavior is too complicated for me to account for with models that don't include such things.

I can describe the behavior of a magnet without resorting to such things, so I don't posit them.

That's not to say that I'm correct to ascribe them to systems with complicated behavior... I might be; I might not be. Merely to say that it's what I seem to do. It's what other humans seem to do as well... hence the common tendency to ascribe emotions and personalities to all sorts of complex phenomena.

If I were somehow made smart enough to fully describe your behavior without recourse to what Dennett calls the intentional stance, I suspect I would start to experience your emotional behavior as "fake" somehow.