Why do animals live in the very cold areas of the world? (why dont they migrate to warmer climates?)?

Animals that live in polar areas exploit the abundant food found in those areas. The seas around Antarctica, for instance, are so rich in food they support millions of penguins and other sea birds as well as large populations of seals and whales. The animals have evolved to exploit these resources with layers of blubber and thick fur or feathers. Arctic seas support the northern equivalent of the penguins, the auks, as well as seals, whales and polar bears for the same reason. Abundant food.