A really large e-bike battery is 4kg. Nobody is riding an e-bike with 50 pounds of batteries. Even the battery pack on a Zero FX, an electric motorcycle, is only 42 pounds.
That's because the motors are pretty heavy as well, and once you have that much torque available you'll need a frame and rear hub that can handle it too. My biggest e-bike is about 30Kg including a 2.2 KWh battery. Not quite 75 lb but getting there. The basic machine is a Riese&Mueller charger with a Bosch speed pedelec motor and the usual complement of brakes, gearing and bunch of bags. I don't mind the weight, but I've yet to find someone else that likes that bike. It's a bit of a pain to move around with the motor off but once you're on it and riding it's just like any other bike only more powerful and it lasts for a really long time on a single charge.
I don't know either. I think part of it is that some e-bike customers are not otherwise bike buyers and go for the niche of huge-wheeled quasimotorcycle. I recommend keeping e-bike weight under 50 pounds because it is the design limit of the bike carriers on American buses and on Amtrak. There are plenty of e-bikes under 40 pounds even.
A really large e-bike battery is 4kg. Nobody is riding an e-bike with 50 pounds of batteries. Even the battery pack on a Zero FX, an electric motorcycle, is only 42 pounds.