> Either way, it's hard to describe anything about a 20 year occupation as "sudden" and having "no transition period". If the US was not able to establish a functional Afghan military after 20 years, what difference would a few weeks/months really make?

It doesn't matter how long you're there for, it matters how gradually you hand over to the locals, and that it be done in a way that supports their success.

This was an abrupt exit after 20 years of carrying the load. Of course it's going to get dropped.