Gentrification vs Prosperity

What, exactly, is the difference between gentrification and prosperity?
I mean if the neighborhood you live in is prosperous, the people around you are doing well and thriving – isn’t that a good thing?
Perhaps the problem is that “market value” is too often being driven by forces that have nothing to do with the individual prosperity of the residents… forces such as “city planners”, zoning boards, and corporate developers.
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