To me at least, the logic rings true. Generally after the early 1960's, Sears began to request changes to the production knives, particularly the fixed blades, to make them distinctive from Schrade's production knives. The Sharpfinger appeared in the early/mid seventies and was a top selling fixed blade for Schrade from the onset. By the mid 1980's, Sears marketing trends had changed dramatically. They still had tents and ball gloves, but got away from hunting and fishing goods. Schrade pretty much handed over the Sears account to the Baer family at Camillus. By then, Schrade was heavily invested in the newest marketing outlets, WalMart and Target, and the hardware chains like Ace and True Value with their Master Mechanic lines. Schrade did use their Sharpfinger pattern as an SFO, but so far at least, I've not seen one marked with a Sears trademark. L.L. Bean, SMKW, Ducks Unlimited... there were quite a few special editions with no Schrade markings.
That is my take on why we aren't seeing Sears branded Sharpfingers.
Michael