Copyright law. Apple's Emoji font is not under an open license for you to copy and redistribute.
The only two emoji sets that I know that are under an open license are now Twitter and EmojiOne
The only two emoji sets that I know that are under an open license are now Twitter and EmojiOne
Symbola font distribution terms: "In lieu of a licence - Fonts in this site are offered free for any use; they may be installed, embedded, opened, edited, modified, regenerated, posted, packaged and redistributed."