Southwest had plenty of older 737s as well, but the new MAX planes both fly farther and have more seats, so while the grounding was in effect Southwest was essentially paying to keep the things on the ground while scrambling to reconfigure their flight network, and it affected them the most.
> why you’d prioritize that over the aircraft’s ability to stay in the air.
This is an egregious misunderstanding. There was nothing wrong with the purpose of the the MCAS system nor the concept of it. What went wrong was its failure to follow the dual path design, and do a proper failure analysis of its design. There was a further problem with some pilots not understanding how to deal with stab trim runaway.
These problems have since been corrected, and MCAS is still on the 737MAX.
They could’ve made a small sized aircraft that had commonality with the 787 rather than the 737.
If the pilots followed runaway trim procedure, which is how the MCAS failure manifested, they would have been fine. In fact, that's what the other unmentioned crew of a 737MAX did that survived MCAS malfunction and landed without incident.
Boeing issued an Emergency Airworthiness Directive about the procedure, which the Egyptian Air pilots didn't follow, either.
If plane going from A -> B is late it cannot become flight B -> C. If crew for this plane are stuck in the ground long enough, they have to wait til the next day to fly as they‘re only allowed to be awake and work for so long.
Distributed systems can also be more complex to re-converge after a major disruption.
I'd imagine it's non-trivial to re-plan a network, given equipment and crew limitations.
And as context, we're talking about 24 hours later, now?
In the event of widespread disruption, planes will not make it to their next airport to become a different flight, nor will their crew. Crew can also only be awake and working for a limit of time, so if the disruption causes a crew to go over that limit they are not going out until the next day, etc.
With cloud computing, it‘s a bit different because which host you‘re using in a region doesn‘t really matter, but for airline a specific plane with specific people need to be in a specific time and place.