.us is only 7 months old. It has been stated here many times that a resale market has not developed yet. If it follows .info's pattern (.info debute a year earlier), a .us market should begin developing within the next year or so. There are still decent names to be found for a reg fee, so most people aren't even thinking about looking to a .us aftermarket now. As names disappear an aftermarket begins developing. Simple supply and demand.