Well, that's because a stock analyst isn't a professional trader/investor and the markets are pretty hard to predict. Overall, Wall Street analysts play a crucial role by setting a baseline range of what to expect.
For the same reason most traders fail, you can give them the best tools and knowledge and they will still do everything they are told not to do, they chase the markets and overtrade, inducing their own failure along with anyone trying to follow them, in the case of analysts they trend the markets and write too much.