This is my opinion about including emoji in Unicode, not the skin color modifiers.
I can only think of it as a case of bike-shedding. Han unification, indic scripts or the lack of differentiation between umlaut and diaeresis are difficult and require experts to be solve satisfactorily. Emojis are easy and anyone is able to contribute a little bit.
What is the scope of Unicode?
Unicode covers all the characters for all the writing
systems of the world, modern and ancient. [1]
Sure, emojis are used for communication, but so are images, logos, emblems, coats of arms. Will we have company logos next? Hopefully not.