Did they give a reason why it was declined? Was it some bureaucratic "form not filled in correct" thing, or are they actually against the concept of it?
To elaborate: it should be plain obvious that not every Emoji proposal can be accepted even though all of them are correctly filed, as there would be too many Emojis there then. So there has to be some threshold, and that threshold is mostly stipulated by vendors' willingness to process new Emoji characters for designing fonts and updating softwares in time.
Since it's a vote, there is no single official 'reason' for rejection. If I had to guess: it would be confusing to anyone who didn't grow up with American TV shows.
I don’t protest the coinage here (goodness knows my native language did worse things to English words), but I can’t stop saying it in Gollum’s voice.
it's a popular image/byword/archetype for conspiracy theorists, idk if it's a common enough symbol to justify emoji inclusion. the submitted proposals probably have analyses of that though :p
So you generally can’t add something because it would be cool or fun or useful, but only because it is currently in use and cannot be encoded by Unicode.
Consider all of the languages it supports. Consider: ﷽ (which isn't an emoji, but the point stands) which is an entire sentence. It was already in use in certain places and unicode decided they wanted to support it, so now they do. Previously, one would have to type out the entire sentence in the original characters, but now it is a single unicode, just like u+263a () used to be alt+1 (). The emoji was already in use long before unicode existed, and in seeing it in common use, they decided to support it.