Price.
I only bought name brands dino and syn when it was on sale with rebate(s). My 1994 LS400 with more than 380k miles had various oil brands in both dino and syn. As of now no engine problem what-so-ever. The MB E430 only had syn, S2000 had syn and dino.
After 20 years and 380k miles the LS400 body parts, interior and exterior, are falling apart, but engine and transmission are in good working condition.