I'm not a moderator, but this is not the way to engage here, and your profile seems to have a lot of the same. You should peruse the comments section of https://news.ycombinator.com/newsguidelines.html or at least try and bring a little more effort to the conversation. You can make the same point in a way that adds light rather than heat.

You could be more charitable. They did say “or” which you omitted in your quote, and also “who knows”. There are possibilities too. In my view, the primary contribution of that comment was to clarify the time frame.

It's based on the fact that we don't know.

We've seen multiple times in archeology when we've originally thought of places as "failed state" or "collapsed" it's actually turned out to be a conscious rejection of that way of life. Most famously Cahokia. Which at one point was a larger city than any city in Europe. We now know that it didn't "collapse" so much as there was a political revolution and people decided to move towards different ways of life.

It's best not to assume failure when you have no evidence for it.

Name fits.