Because changing environment unintentionally pressures previous long-standing residents into leaving the area, and causes discomfort as two divergent groups mee

Because changing environment unintentionally pressures previous long-standing residents into leaving the area, and causes discomfort as two divergent groups meet in the same location and one feels the other is destroying, ruining, or usurping their culture. It's not "bad" as a moral stance, but certainly some claim it is bad from their perspective if they end up on the losing end of gentrification. To give an example that more people might empathize with. Parts of central London used to be affordable by the mid to upper classes, but these scenic locations are now 100% owned by others who only buy them for use as vacation homes. It's an odd case of gentrification pushing relatively wealthy people out of an area so that extremely wealthy people can live there instead.