There's a bit too much to go into here, but we can start with two non-human error crashes killing hundreds of passengers (i.e. the planes flew into the ground). Then there's the corruption and collusion involving US federal regulators and Boeing to cut costs to certify an inherently unstable plane (very briefly: the engines are too big for the original 737 design and too far forward), as well as the subsequent attempts at covering up responsibility and trying to blame pilot error. I will do my best to avoid boarding one of these flying coffins. Aerolineas should have cancelled all the MAX orders and bought Airbuses instead (and to Quilombo, AA probably received huge financial incentives from Boeing for not canceling the orders).
If you're interested, this might be a useful introduction to the topic:
https://www.theatlantic.com/ideas/archive/2019/11/how-boeing-lost-its-bearings/602188/ Lots of other articles and information out there, as well as posts on avherald.com and pprune.com.