Eli5: Why were the Boeing Max 9 planes immediately grounded but not the Max 8’s?

Question

I don’t understand why regulators immediately grounded the Max 9’s, but it took two Max 8 crashes before they were grounded.

In: Other

Answer 1

There was disagreement (and considerable pushback from Boeing) about whether the first Max 8 crash was due to a design flaw or pilot error. It wasn’t until the second crash that it became irrefutable that there was a catastrophic flaw in the software.