Because aside from small amount of people, like Russian scientists, no one has really tried to domesticate foxes. Those foxes are the result of of 50 or so years of selective breeding, and as you can see, they became a lot more dog-like. They're still not quite there yet like dogs are, though. Keep in mind dogs have been domesticated and kept as pets for tens of thousands of years; these foxes still have some wild tendencies even though they're tame. But who knows, give it another few years and maybe pet foxes will be more common.