Why are Ben Stiller and Owen Wilson always in the same movies together?

Okay there not part of Happy Madison, they make way different movies, Happy madison work with Adam Sandler and the rest of his possi. Ben Stiller and Owen Wilson work with Will Ferrel, Vince Vaugh and Luke Wilson. They just amke great movies together so i guess that why they do it. Plus they are obviously friends. They also dont JUST get the roles b/c their friends, the movies they work in tehy are usually co-producing it or writng it, so they usually consider these actors first for many of the roles.