Because some people are not right in the head?
Just earlier today I was playing, I had high scores, almost always at the top of score board, did not teamkill, did not chat at all, just played for a while.
Later when I had to leave I asked a buddy to do a poll on me to check it out. He did a poll to kick me and it passed. No reason for kick was stated, I did nothing to anger anyone and I was helping my team constantly and had high scores. A poll still pulled through on an almost full server.
That only shows how retarded people can be.
I was just amazed at it, not angry.