Why do Europeans have them while Siberians don't?

Obviously they can only evolve in dark northern climes, but Siberians lack them.

Also they used to be even MORE common, 100% in paleolithic europeans. They were also heavily selected after the bronze age, the Aryan invaders were almost completely dark-eyed.

So what advantage did they give to paleolithic and post-chalcolithic europeans alike? And why was this advantage not experienced by Siberian people on the same