It's probably on clearance because many of Crest's toothpastes contained tiny pieces of blue (and other colored) plastic that weren't getting washed away. On a pretty regular basis I find little blue specks in patients gums as were Hygienists around the country. There was one who called Crest out on it and their answer was: It was a color additive.
There is no immediate health concern with the plastic, just that it doesn't dissolve and doesn't deliver any sort of medicament so why is it there? Oh, because Crest thought it looked pretty that's why.
They are phasing out the use of the little color specks by this May. I usually like Crest, but this was pretty shady IMHO.