I teach in south central Los Angeles. The congregations in this area are very "healthy" and thriving. I have had a few fake studies with Black brothers from the area and have attended the meetings there. I have concluded that there just isn't the same kind of mass exodus/awakening from the WT in black congregations that we are finding in higher socio economic areas. Uneducated inner city blacks just don't have the tools available to them to challenge the WT. Further, the WT is very, very appealing to disenfranchised blacks in poverty because with out any sort of education at all, you can become a WT heavy in your own congregation.
The doctrine that if one puts spiritual things first in life all other things will be added to you is also very appealing to poor people because it suggests economic stability. So, live a shitty life in south central, have your kids join gangs and take drugs or become a JW and become a "respectable man with economic stability." It's a no brainer. Becoming a JW or staying one will always be a better deal to inner city black folks. A mass exodus in the black community is very, very far away.
I grew up in South-Central. I know many elders in the area. You are right to an extent. Because the Spanish Congs. are taking over the area. many blacks have migrated to the outer areas of LA and become inactive. They have seen the light in some cases. I know of MANY that start off strong and fade away sloooowly. They see the wealth and big houses and start to work Overtime. Many in LA are taking meds because of the depression and guilt. As mentioned, you are definitely correct in your assesment!!