That eight inches is called "side impact protection" and, while it sucks to not be able to comfortably rest your arm on the window sill, it is pretty important to have in the event of an impact to the side.
Safety people: <Ruins cars>
Also safety people: "These goddamn consumers have started buying SUVs"
I'm not saying this is you personally but the trend is pretty goddamn clear.
I liked it when my car could fit inside a parking space, personally.