Because Tesla makes the best electric cars and as they reach economies of scale total cost of ownership will dominate fossil fuel cars. They need to lower price

Because Tesla makes the best electric cars and as they reach economies of scale total cost of ownership will dominate fossil fuel cars. They need to lower prices now because Teslas are still relatively expensive compared to, say, a Toyota; but in the long run they won't need to lower prices further than a certain point. Plus Musk sees angles that few others do and a platform of mobile sensors operating around the planet is inherently comercializable.