Yeah, I never have understood it either. I mean it's not even a character. It has no personality, it's not self aware. On top of that, it's not even a terribly interesting design. But so many people behave like it's one of the greatest characters to come out of Sunbow.
I recall this whole fascination with Nightbird even from the early days of online fandom. Back in 91 - 92 there was a strong tendency amongst some elements on A.T.T to treat Nightbird as a very significant character, scouring the episode for the slightest thing that would prove that she was a freewilled creature who wanted to join the Decepticons to be free from the oppressive forces of her creator and the Autobots who wanted to treat her as a slave. (Some went further and stated that Megatron was clearly in love with her, and had put her in stasis at the end of the episode so that she could heal... This latter one was propogated by females, for the record...)
It is...just something I take as read in TF Fandom to be honest.
Its just not a great mould. It does look good as Slipstream, arguably better than TFCC effort, but a bad mould is a bad mould.
BA on the other hand is a mould I've thought for ages was not only great but should be brought over to the classics line. The remoulding is fantastic.
Hopefully a few other Animated moulds will get the same treatment. I've long said that Animated ratchet would require only minor changes to make a far better classic Ratchet and Ironhide than we've had so far. Prowl isnt far removed from Chromia in style, though what they'd use the mould for I'm not sure. Cybertron Prime for Thunderclash also springs to mind.
It's pretty damned sad when a ten year old pre-classics repaint of an energon mold is STILL the best G1 Ironhide and Ratchet, beating out the actual Classics styled mold AND THE FRIGGIN MASTERPIECE MENT TO BE THEM from the start! Beating the actual MASTERPIECE.