After all of my internet research, I finally went to the source of the great paste mystery. I emailed Elmer's with my query. This is what I got back:
Thank you for contacting us regarding Elmer's products.
Unfortunately, that product has been discontinued and is no longer available. We are sorry for any inconvenience and disappointment.
Consumer Response Analyst
That's it?! No explanation at all?! What a disappointment. I bet Brian Rumschlag doesn't even know why paste is off the market. I bet he never made fabulous masterpieces out of construction paper, glitter, macaroni and paste when he was in kindergarten. What a shame.