Why are citizens from Great Britain not allowed to apply for the U.S Green Card Lottery?

Considering the Great Britain are U.S's biggest allies, why are we not allowed to enter for the green card lottery? (except northern ireland). Citizens from Afghanistan are allowd to apply, even citizens from Australia, France, Germany, Switzerland are allowed but for some reason UK citizens are not. I know there are exemptions such as where your spouse or parents were born but what if you and your parents and your partner are Bristih born and raised - it doesn't seem fair! What is the reasoning behind this? Is there any other way around it? Can you appeal to the American emby?