If someone knows otherwise....please chime in:

"Synthetic" oil is a bit of a misnomer, the molecules that make up these oils are still petroleum based but they are (more or less) harvested or "Cherry picked" molecules that possess whatever desirable qualities for strength ,lubricity and ability to withstand temperature extremes they are looking for within that particular viscosity...or base oil from which the viscosity is derived from.

It's more likened to making wine or beer than anything "magical" only instead of grapes or hops they are cultivating molecules with the most desirable properties.

"convetional" oils are held to a much wider broad base where the weaker base molecules break down faster from temperature extremes and shear forces when under normal driving conditions.

So it's more like screening and selecting the Varsity team verses a scrimmage team that consists of more (possibly better in a few ways but worse in more other aspects) random skill players.