The reason: hallucinations.
When I demoed ChatGPT to my undergraduate engineering students on Friday, I asked for a question from the class. One is illustrated above: Seattle and Washington temperatures in 2010. Students quickly turned to Dr. Google to fact-check ChatGPT. Big oops, there, OpenAI.
New policy: suspend any account which references a banned account in the account bio or display name. Probably also just Mastodon.