Not sure why it has the rake to it, but would like to see that gone.
Not sure if you've actually used the cargo compartment for hauling stuff.
When I moved the contents of my apartment across 943 miles, it became readily apparent - the rear was sagging more than the front.
Toyota probably designed the FJ Cruiser with the assumption that the rear cargo space would actually be used for its purpose - and whatever weight in there would level it out to some degree. If they designed it level with the same assumption, the rear would be sagging all of the time.
It's just more aesthetic to have a drooping nose rather than a sagging butt.