Sperm whales are found in many areas around the world, but it's actually very rare to see groups of sperm whales around Southern California. They usually prefer deep, off-shore waters and have denser populations near continental shelves. For more about sperm whales and California, see this website:

For more about sperm whales in general, see this Wikipedia article:

For the same reason other whales come here: a deep ocean near shore that has a lot of food available.