Just like how BMW is known for performance, Tesla is known for electric vehicles. That's their product and people trust in that brand for that, so BMW may never unseat them from the top. But it could overtake the Nissan leaf if one of their EV models are priced right.
That's such a vague response and shows a lack of knowledge in the brand on things that can be picked up on easily just from face value. Tesla's are semi-luxury higher performing EV's and once BMW and other car makers release their own EV of similar caliber then the challenge will be on. Why might BMW never unseat them?