There are activists in Black countries, you are just more aware of the ones in the west because of the language barrier and exposure.
And for those who migrate to the west, they do it for economic reasons and a promise of a better economic situation, it's no different anywhere else, It doesn't mean they dislike their country or they lack pride. You see Somalis back migrate for the same reasons. It doesn't mean they don't stop advocating for their own as soon as they leave their country.
The truly broken are the ones that spend time maligning and forsaking their own.
It's like saying Jews or Zionists living in the west advocating for Isreal don't want live in Isreal. Or Palestinians being activists living in America don't want to live in Palestine or Gaza.
I suppose the small Somali population in New York doing political activism for Somalia/Ogaden in the 60s is because they don't want to live in Somalia