I think the idea is that once it's published, it's very difficult to withdraw or change the text. If you were changing the text, then the people who signed it previously may not have signed the same thing. The change may seem insignificant, but for some people it might be a big deal, so we don't change the text and we generally don't withdraw petitions once they're published.
On February 28th, 2019. See this statement in context.