I asked something similar a few months back when comparing Pennzoil Full Synthetic vs PP and PUP. Guess we’ll never really know, I’m sure a lot of it is marketing to get you to buy the higher tiered oil. But could also be a cheaper base oil and additive pack. Biggest difference I saw when comparing the Mobil Synthetic vs Mobil One is that the Mobile Synthetic is rated for 7,500 miles and Mobile One is rated for 10,000 miles. I usually change my oil every 4-5k anyway so I just roll with whatever is cheapest at the time of purchase.