Because you can't legalize equality. There will always be people who are prejudice. It's life. Learn to deal with it. We are all prejudiced in some way, even if it's against other people who are prejudiced!
But in the same token, there will always be someone who wants you for who you are. Those are the only people that matter anyway.
Why waste time with the assholes?
Now, government policy and public policy is different than private affairs, and there should be the same guidelines for everyone no matter what.
But you're not going to stop prejudice by all this PC bullshit. If anything, that just adds fuel to the fire.
Lead by example, defend the persecuted, and stop expecting government legislation to fix all your problems.