My guess is that its for the same reason phones battery life hasn't really changed much over the years: the current range is enough for most people. 300 ish mil

My guess is that its for the same reason phones battery life hasn't really changed much over the years: the current range is enough for most people. 300 ish miles is enough for local driving for a few days without worrying about recharging, and enough that most people will need to take a break when driving long distance more often than the car needs recharging.