Negotiated rates help in case room rates go up. You are locked in at your rate. Unfortunately covid happened so rates plummeted. Im sure these prices were negotiared a long time ago. On the other side if SP booked another big convention during the same time and then their normal rates went to 300$/night we would still be locked in at our rate.
So dont blame who negotiated the rate. Rates constantly change. At the time of negotiations im sure this rate was a deal.
You should be thanking the hard work put into the convention planners and them volunteering their time to make it happen.