I am not going to refute your statement but I would have thought that the rising economic viability of the black community would have kept the retail arena alive. I'm sure there are some factors I am not aware of in play.
The black community began to rely on their own retail and service businesses. They became more self sufficient. The effect was much like when the black community in Atlanta stopped riding public buses. Returning black vets from WWI were a boost to the local economy and weren't willing to accept the degradation they suffered pre-war. Greenwood was quite prosperous and was a threat economically to the rest of the downtown area. They didn't give up their jobs as elevator operators, servers, etc. they merely kept their spending and investing "in house". Bear in mind, the entire area, buildings and all were razed. It wasn't just racial.
I believe most riots, wars, coups, revolutions are economic in nature. This one had significant economic determinants.