Good question. In some other analyses it looks like interventions that are designed for and delivered to African American MSM work well.
The problem may be that for various reasons, the men of color in majority white studies don't feel like the intervention is really addressing them. For example the characters in videos may be white, or most of the people in their small group meeting are white, and they don't feel like they are facing the same set of issues, so they don't connect as well.
I think as a gay man I often feel the same way about messages for straight audiences. It's not that I don't like it or whatever, it just doesn't seem to apply to me.
Just a hypothesis for now ...
it has only been in the last few years that I have started noticing commercials and such using people of color and it makes me think of how THEY must have felt all those years when all the models were white.
That does sound like a good hypothesis...(HA! I know that one!!)
I wonder also if it might also be cultural? do you see a difference in white men that live in cities for example vs men that live in rural areas?