If Marriott could sell a room, they had rooms. It just wasn't a POINTS room.

Exactly. As a for profit business, Marriott (and other vendors whether hotel chains or air carriers) doesn't give away the last room/seat for free. Those are capacity controlled. As OP found out, there was a room for $379. Whether that's good value or not is an individual matter. Me, I would have grabbed it in a split second, paid it and submitted the receipt for whatever I could get back (likely whatever the carrier pays at PHL for IRROPS rooms). The vagaries of travel.

Many airlines will only reimburse a hotel room up to the value of the hotel vouchers they distribute or the deeply discounted contract (or distressed traveler) price they pay if they book someone into a hotel.

You've never heard of SPG? I've booked $450 Christmas week rooms at ski resorts late in the year. The "if there's a room available, you can book it on points" policy has been around a long time and is a very significant differentiater from MR.

Other chains have caught on an matched them. MR continues to obfuscate with the "no blackouts" claim which this situation shows is a pale shadow of the others.

Should you be upset with Marriott? No.

Should you feel frustrated with the overall situation? Yes, I empathize with you, especially if the person you were doing this for is not a road warrior.

Marriott platinum line can only pull strings when there are strings to pull. When something happens at an airport, rooms can be booked - very fast. One call from one airline agent/supervisor can book dozens of rooms. Room go to rack-rate quick and disappear.

Back in the day IAD had this often. One night I took a 45 minute cab to a hotel and another I booked the last room at the IAD marriott - 2000 sq foot 2 bedroom, 3 washroom suite with a full dining room and a large bar / kitchen. $500 - reimbursed by CC travel benefit.

My challenge when this happens is do I keep trying to find flights (other connections, other nearby cities) or do I book a room in the city I am in and accept the overnight? This is where status comes in - I usually book the local room and if I get on a flight call the platinum line to book a room at the new city and cancel the local room, which they can usually do, even if it is after cancellation time... that is the string they can try to pull because you are moving from one marriott to another.