For reference there were only 52 of these planes made compared to 171 max-9 varients
[0] https://en.wikipedia.org/wiki/Boeing_737_Next_Generation
And that’s United only. They were manufactured for over 10 years.
People are ACTIVELY flying these aircrafts by the thousands each day. It's these people, these human beings, that are to be saved from a potential crash. Not Boeing, not the manufacturer.