<p>I do not know for certain.</p>
<p>I can speculate, however. I think that some of it might be that talented whites and Asians go into other fields (engineering, medicine, business, i-banking) at significantly higher rates than blacks. So a lot of them are being siphoned off before law school applications are even in mind. (Law school, in a lot of ways, attracts the "best of the mediocre" people. There are some really freakin' brilliant legal minds out there, but the majority of the people don't have any particular aptitude for the subject.)</p>