I don't think it's all Boeing's fault. Aircraft mechanics (like pilots) are in short supply and overworked. There's quite a bit to maintain on a jet and you can't really test it before you put it back in service. They may have missed something.
So Boeing not hiring and training enough mechanics is not their fault? Whose fault would that be?
Part of it is. The door plug was clearly Boeing's fault, along with the subcontractor they used. The door was installed improperly, not inspected properly, and as a result blew out. With a loose panel coming off, that could be the airline, or Boeing. In Boeing's case, it might be a design flaw that needs fixing. Or, the airline mechanic didn't reinstall it properly after maintenance and the like. Hard to tell on that one.