Beyond me.
Don't assume that they are all real. These inflammatory comments make people come back to the page ($$$).
I know for a fact that on YWN at least some are manufactured. When I see this trash in other places, I assume the same.
ETA: I haven't looked at the VIN comment section in many years (if ever), but I just checked now. That section is trash. They should really shut it off, but that's probably not gonna happen.