They're great for some people. People that have multiple vehicles, live in the city or don't commute far, own a home with a garage, and can afford to travel without using the electric car. That's not to say other people without those luxuries can't live with an electric car though.
The most popular electric cars still carry a premium price, although there are a few that are very affordable, like the Fiat 500e.
Also, they couldn't be best sellers. They just can't. There isn't the production capacity to make that happen.
Expect electric car sales to keep climbing as battery technology improves and battery prices decline. Any day now, Panasonic is supposed to release an updated cell that will increase capacity by 17%. Then things will really change when lithium air batteries are commercialized. As that happens, more automobile segments will be filled by electric cars.
I'd love to have an electric car to drive around most days of the year, but it'd be difficult for me to afford those days of the year when an electric car isn't suitable. Having multiple cars is something I'm trying to move away from, both because of expense, and because it's a hassle to take care of more than one car. Something like a Chevy Volt is nearly perfect for me. I could use it primarily as an electric vehicle most of the time, but because it's a hybrid, I can drive it well beyond the range of the electric battery. Take the Chevy Volt foundation and refine the technology for a couple generations, and it'll be serve as the underpinnings for most of the vehicles I buy from then on.