But in this case I would argue that the leasing company is not delivering the product, the airplane.
I I do a leasing for acar and the leasing company cannot deliver I would not pay.
If I take a bank loan for purchasing a car, it would be my problem.
Lease payments are typically due on planes that have been delivered and are in the airline's fleet. Leasing companies don't usually have piles of cash lying around that they use to buy planes from the manufacturers. They're using investors' funds, and said investors don't stop expecting a return just because Boeing bungled it badly. For all you know, a mutual fund you own has invested some of its cash with Avalon. How much of a haircut are you willing to take so that Avalon can stop collecting lease payments and suspend paying dividends to your mutual fund?
Planes that came out of the assembly line after the model was grounded have not been delivered, and no payment is made or due on them (other than Boeing paying its suppliers)