As others have said, it more about what's not in it. Wet clutches are designed to be used in an oil bath, so the oil itself won't hurt engagement of the clutch. Beside that, it is just about selecting certain types of additives for the required performance and avoiding certain other ones that could be used for those same purposes, but would negatively affect the clutch performance.
The key to making a good motorcycle oil is to try to get the best total performance, for engine and transmission, out of the additive types that won't hurt a clutch.