Efficiency. The lightest electric cars are twice as efficient meaning heavy cars have massive global warming implications.
How can we be post oil economy when energy usage is double what is needed?
Your humble electric bicycle will be at 10 to 100+ efficiency. If the whole world owned a car as little as 10 years ago I doubt many of us would be alive now.
Less important in big picture terms; but heavier vehicles also do more harm in crashes, and wear out our (expensive) infrastructure faster.