User blog comment:The Smarter, Wiser King Dedede/The show has been renewed for a fifth season/@comment-38567889-20190507213241/@comment-33001101-20190508034531

Because if you read Season 5's background, it will announce a big change by having Lori and Lincoln graduating.

Also, theoretically, this would have been a 3rd time a future season to be announced before the next season was about to be aired. Season 4 would have likely been announced before season 3 aired, my guess was that it was due to Chris' firing that caused the production schedule to be extended.