Because social media are owned by rich people and racism is among the oldest tricks in the book to get people to act illogically in elections. If people in any given country were reasonable, they'd vote for their own benefit. As most people in our modern society are employees, all logical options to vote for consist of left political parties because the parties on the right side are all about transfering wealth from the normal people to the rich.
Racism is an appeal to hierarchy. It's about moving minorities down the ladder and having the majority (which happen to be white people in most democratic countries of this world) sitting above without any accomplishment or merit on their own. For a surprisingly large amount of people that is worth the sacrifice of their own wealth and they will even believe that they are behaving reasonably despite hurting themselves again and again and again.
Legend11 correctly predicted that GTA IV will outsell Super Smash Bros. Brawl. I was wrong.
