The only reason airlines are backing the MAX is that they need to get their fleet back in the air and keep them flying, they are dependent on them and can't simply switch. It's like being stuck in a bad marriage, walking out is easier said than done. Airlines that already have a significant percentage of their fleet in the MAX or have a major future commitment to the type must be getting desperate for a solution. Imagine the effect on a major B737 operator such as Southwest Airlines if the MAX is permanently grounded and they're faced with waiting years for an all new Boeing narrowbody or switching to Airbus with a years long waiting list.