On all Nick/Nick Jr. shows, they always use split screen credits with upcoming previews to close the show. Now that they recently added that policy to all live action Nick shows (Drake & Josh, Ned, etc), Blue's Clues is the exception & exemption of that policy! The sole survivor!
NBC started this whole split screen credit policy back in 1994 on all their programming, except Days of Our Lives (which finally caved in around 2002).
"Like sands of a paw print, these are the Clues of Blues! This is your friend Joey & these are the Clues of Blues!"