For some reason, people ignore the sign and do it anyway.
People ignore signs all the time. Signs have no way of enforcing the law or what they are intended for. We dealt with speeding cars and cars not stopping at marked crosswalks all last weekend. Unless there is actual enforcement, the sign is taken as just a suggestion.
To Bob Dot...if there could be a heavy clear barrier used as a deflector, you would still be able to see but there would be protection. Yes, it might also cut down on the number of people ($$$$$) and that is probably why it will never be implemented.