Diamond Elite does not guarantee preferred parking. Just says it's subject to availability and you must make a reservation no later than midnight the night before. Mid-day Friday was after the deadline. I am sure SFMM has some sort of ratio for spots available vs. spots they are going to sell (or use the reservations to calculate how many they can sell after taking reservations out of inventory), so if all the reserved spots were taken up by people who DID reserve in time (but may not have arrived yet), all that is left if the spots for sale.
The only thing you can arguably fault Six Flags for is that "midnight the night before" could be taken as up until midnight the day of visit, not midnight the start of the day before you want to visit. I read it has midnight the day before you want to visit, not midnight leading into the day of your visit.
So good for SFMM for taking care of him.
Then I clearly misinterpreted it. My apologies. Agreed nonetheless: good on SFMM for responding in the way they did.