What is an example of a hypothesis which may explain why there is not a big representation of the class Reptilia found in polar regions?

Beings of the class Reptilia are abundant and more varied in hot climate regions and they are rare in intensely cold regions like close to the earth poles. This is defined because these animals are heterothermic, i.e., they have "cold blood" and they require an external heat source to warm their bodies.

The heterothermic feature also defines why reptiles are more active during the day, a period when they can use the sun heat to warm their bodies.