It's a two-month old plane. That's not much time to fall into disrepair.

Yeah must admit I think I jumped the gun a bit there. Reading about it a bit more it seems like this is a major manufacturing cock-up that this was even possible.

If an inspection done after going into service involved removing/replacing that door, it could have been done incorrectly.

There really is no way to know what happened without more research, and I’m confident the priority will be to understand if this was a one off or widespread issue.

Aren’t maintenance protocols handled by the FAA? Otherwise it would be implied that budget carriers like Spirit or Alaska would be “less” safe (which isn’t the case AFAIK).

In what way is Alaska a "budget carrier"?

Maintenance protocols are a mix of manufacturer recommendations and carrier/maintenance contractor SOPs, which are then approved by the manufacturer and FAA.

In 2000, an Alaska MD-80 went down, killing all 88 onboard. The NTSB found that it was apparently due to failing to adequately lubricate the tail jackscrew, as required by manufacturer documentation, not just once, but in at least two successive scheduled maintenance periods. Also, Alaska had been increasing, with FAA approval, the period between scheduled maintenence. See https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261

This plane rolled off the factory floor in October. It’s brand new.

sorry, but this one’s on Boeing.