Lots of things can cause hands/feet to be cold.

Cold core
Cold limbs
Restricted blood flow
Maybe cold head, I'm not sure
Poor circulation

And of course simply insufficient insulation at the hands/feet to keep the warmth in.

This past Sunday I rode 9 hours in temperatures from 28F to 40F. Depending on effort level and wind exposure, my experience included bouts of cold hands, cold feet, and perfectly comfortable. In my experience that's just how it is.