They have more than 5000 orders for this model of aircraft. Each one costs approx 120million. Which means there are approx $640 billion dollars on the line. It is imperative that Boeing keeps it's reputation and grounding flights would destroy it.
If anything, it's a huge positive if they grounded it until they knew for certain what's wrong because then it's a double win. Firstly, on the ground the plane has a 0% chance of killing anyone (unless someone decided to jump off the top of a parked plane and commit suicide, etc.), and secondly Boeing's reputation goes up because now people have a chance to think "ok finally, they actually care about safety instead of profits".
Also, Southwest is the largest US flyer of this plane and it only makes up about 5% of their fleet, so it's not like the entire world's flight traffic gets disrupted. Lastly, I would think most people who are scheduled to fly on one of these planes will cancel or demand a plane switch, so the delays and flight traffic issues are still going to happen to some degree.
Currently, all I'm reminded about from this situation is how insanely corrupt the US govt is (I'm from the US btw) and how little Southwest cares about people because they won't even let you cancel without paying out of pocket, which is totally insane. You only have 1 life.
Too late now though. If the truth comes out and it's not a Boeing problem, their reputation suffers for "what might have been". If it is, their reputation suffers for "profits over safety"
Southwest, for what it's worth, were offering free changes of ticket for those on a max. American weren't.
Now it feels more like a calculated reaction based on profits (ie. enough people cancelled MAX flights or asked for a flight change that grounding the plane is now a better decision financially).
In any case, it's a good result that they are grounded until everyone knows what happened during the crash and have an iron clad solution to prevent the same thing from happening in the future.
Yes, because by now, every pilot still flying that plane has been trained to deal with the issue.
If this issue did occur again (and that's not proven), the question is why didn't the pilots deal? Were they operating past their limits for whatever reason, like with UPS1354? Or is it that the problem isn't something that can reasonably be dealt with.