Just my 2 cents. As an owner of an IHG hotel in silicon valley, I can believe that there were no hotel rooms available during the Op's date. There have been plenty of days like this in the Bay Area.
That said, Its unfortunate and unacceptable the OP had to sleep in the car.
I put the blame on Marriott and the hotel here. 80% Marriott, 20% hotel. Why u ask? Well, Marriott like other brands are similar when it comes to res systems and all the channels that are fed thru their systems. ( 3rd party websites, corporate websites, apps...etc.) Rates and inventory have to be synchronized all the time. I have seen this happen alot. The hotel may have been sold out but the sync didn't take place, or a walk in cane in at the same time the OP made the resi, or simply Marriott dropped the ball completely
#1 - they should have walked the guest with a guarantee reservation at the hotels cost. With the perks.
#2 - Marriott customer service should have given ANY option. (70 miles, 80 miles?) OK didn't mention any details about what customer service was looking at during the call. Did they acknowledge the reservation?
#3- if the hotel did receive the reservation on their end after it was made. Then they should have contacted the guest right away and inform them that there aren't rooms available and ask the OP to contact Marriott directly. (20% blame)
#4 - the next time OP is in Silicon Valley, we would be more than happy to rent them a room at my IHG hotel. Lol...with a 25% discount. ( PM for info)
hope all works out in the end. Ultimately, the hotel will get dinged any money or points credit you receive from Marriott anyway, always happens..