Well, their review process and requirements for sourcing should ensure that it's factually accurate, no matter how it came to be. I imagine, they also have broader policies already, like that the submitter has to ensure factual accuracy and that they own the copyright.

This explicit ban is presumably just because the other policies got violated so frequently, when an LLM was in use. Well, and maybe they also got tired of reviewing as much texts as the LLMs produce. Unfortunately, the article is paywalled, so I am just spitballing...