Why do people message you "Hey" ?

I don't know why it bothers me so much..But I really can't stand when I go to read a message and all it says is "hey". Like "hey", could you not think of the rest of the sentence you meant to send? How RUDE! Sending me a message and expecting me to be the one to carry on a conversation with you is asking too much! Next time think out exactly what it is you would like to say/ask. With that being said....This post is not a invitation for all the people who know how to write complete sentences to inbox me.