Because you can't ride a battery mower. You also can't get the same power as a walk-behind (e.g. Swisher) with batteries. Gasoline has much higher energy density than batteries.
Hey, Palmer. Can’t you just step away from logic and reason for a moment, and embrace your inner unicorn and rainbows?
>> You also can't get the same power as a walk-behind (e.g. Swisher) with batteries. <<
Yes, you can. Some battery mowers have as little as 18V motors, giving them a bad rep. But 80V motors are getting more and more common. So many FReepers have bad experiences with bleeding-edge tech, and then write it off permanently.
>> Because you can't ride a battery mower. <<
I can't vouch for them, but they do exist. Ryobi RY48110, for instance.