content: Because lithium batteries are still pretty expensive (IIRC it's ~$200/kWh even at high volume wholesale prices, assuming a bus uses 5x as much power as a Tesla Model S, that's 80 x 5 = 400kWh = $80k for the batteries not including battery management etc.) They probably did their research and found that 90% (or whatever) of buses do less than 350 miles/day and so that's enough for now.