Emotionless?

Again I am sorry I haven't been around lately. Finding a job is exhausting. But this isn't about that. It's about this:

Now this video has really got me thinking again about something profound that I missed the first 50 times I watched it. Why is it in this song Celestia shows a HUGE amount of emotion about remembering when her sister slipped into rebelling against her, when in the series not even a single tear was shed when Luna returns in the Friendship is Magic Part 2 episode? All she does is tell Luna to ask for forgiveness and "hug" her to finish it. What? Does Celestia not care that her own sister, that she had banished a thousand years before the series kicks off, has come back? Either she has no heart or she just doesn't care. Why is it that when we interpret what happened a millenium ago we express this as such a gut wrenching event, when in the series it's shrugged at like they did with the Ursa Minor or Cerberus rampaging in Ponyville? It's just another day in Equestria. And even in the recent aftermath we see it as a HUGE ordeal. Why?
Well, I think it's because we, as dedicated Bronies and Pegasisters, or just fans in general, feel that this ending to such an interesting story plot element(and the origins as well) are so lacking that we HAVE to fill in the gaps of what happened. We HAVE to know how and why Luna became Nightmare Moon. We HAVE to know how Celestia felt during all those years of ruling alone. We HAVE to know how all of this affects Luna. It's in our nature to do so. We HAVE to explore this world deeper than what is given to us.