Tesla wisely is going after premium buyers, that market is niche by definition. They've done that because car is a major purchase unless if you a lot of money and you are more willing to take a chance on a new car company.
But beyond that, it doesn't matter if Tesla is building a better car, it matters if consumers think Tesla is building a better car. And tesla doesn't have the same brand loyalty in a very competitive market.
Secondly, if you're buying an electric car for environmental or gas price reasons, there are other options. I can lease a Nissan Leaf now for $199/month. The amount of money I save on daily gas cost driving my Honda will almost come to $199! It means I can have a car for 3 years for free (minus the $2000 singing fee). Tesla just can't compete with that!