Probably a number of reasons, including the insightful ones posted above. Maybe three more:
1. Since syn can cost 3-4 times more than dino, potentially doubling the cost of an oil change, this might leave a "bad taste" in consumers' mouths that auto marketing departments want to avoid.
2. Even with syn, externally-introduced dirt and internally-produced soot will still tend to turn oil into chocolate milk by the 7,500 mile mark and beyond. So while syn has better shear, decomposition, and temperature qualities, it's not a cure-all: It will dirty from particulates just as fast as dino.
3. Syn isn't what it used to be after Castrol Syntec's b*astardizing of the species, watering it down to something resembling a syn/dino blend, and Detroit knows this.
[ March 06, 2004, 05:29 PM: Message edited by: TC ]