My theory is the flagship product is still, after many years, PYB.
So they have no qualms about dumping excess GTL stock into yellow bottles to get rid of it, as Synthetic oil still isn't a big seller compared to cheap dino.
And, if anyone "finds out" this is what is happening, well, Shell can just say, "We told you it is awesome oil, not dipstick marketing."
Also, I would guess that the "cheaper" add pack of PYB gets a boost from being blended with, bar none, the best oil basestock currently on the market.
Also, the ultra low Noack would help out with Pennzoil cleanliness claims, by just not burning off and adding to a dirty engine even if it isn't really cleaning much.
I ran PYB before my current fill and it was really quiet oil.
I have ONE jug left, I wonder if there will be another $9.99 Walmart Boxing Week sale on the PYB 5L jugs again!!