I'm a bit confused by this. From what I've read an "airworthiness certificate" is not a certificate that the aircraft design is good and safe. That would be a type certificate.

The airworthiness certificate is issued for a particular aircraft and certifies that it conforms to the approved design for that type of aircraft, all outstanding airworthiness directives applicable to the type have been applied, no unsafe alterations or repairs have been made, all required documentation and logs are present, the inspector doesn't see any damage, leaks, or other problems that could make it unsafe, and other things like that.

The two 737 MAX crashes had nothing to do with anything that would have been found during their airworthiness inspections. They were functioning exactly as they were designed to, as covered by their type certificate.

So what was the point of suspending Boeing's authority to do those inspections?

The main motivation for recertifications comes from commercial pressure where if a aircraft is given a new number and not recertified, then the pilots have to be retrained.

Honestly, back when the 737 MAX debacle happened, a lot of consumers claimed that they would stop flying aircrafts if they ran into 737 MAXs. And I don't think it happened in enough numbers - or even enough to make news. Sales went through the roof, everything kept working.

Recertifications are very common. The issue really is is the aircraft is AS different and untested as the old MAXs, and I really can't see that happening again in the next decade or two atleast.

This is well outside my knowledge domain so I'm not trying to make any statements on whether this was correct, but rather to better comprehend the change.