Why arent there many reptiles or amphibians in the tundra?

Most reptiles are cold-blooded and have a low metabolism, which means that they must rely on the heat of the sun to help speed their metabolism. In cold places, such as the tundra, a reptile would most likely freeze to death and would not be able to move very well. Although there is a certain species of frog whose blood contains some sort of anti-freeze agent and allows it to hibernate in suspended animation... Well, that's another story.