An article in the Chicago Reader, a few years ago, addressed this statistic.
A "gay-friendly" organization sent undercover reporters into gay bath houses to observe and note the occurrence of unprotected sex.
What they reported was this: Black and Hispanic men had unprotected sex at a significantly higher rate than Caucasian men. This was at a time when various organizations had begun a major initiative to influence homosexual men to use condoms.
That's reason #1.
Reason #2 is mentioned above by another FReeper: "Down Low".
Reason #3 is IDU - Intravenous Drug Users.
Reason #4 is the typically-African desire for "dry sex"
Feel free to add any other reasons.
That would seem to be more than enough right there.
And EWW!