The documents in the link that the post is about are from 2021/2022 though. So they must have un-banned it. The "guidelines" document at https://www.amtrak.com/content/dam/projects/dotcom/english/p... lists 44 Amtrak stations throughout the US where this practice is allowed (and likely to continue to disrupt schedules for regular passengers).
It's infuriating actually. There are plenty of historic railroad societies that own track around the US where people can take their railcars to be driven around. Amtrak has a credibility problem because of its reputation for being unreliable, and this affects public perception of passenger rail transit overall and how worthwhile it is to invest in it.