When I'm driving, I try to be alert for motorcycles but the roar of their engines usually alerts me that one is nearby. Without that roar, it becomes much easier to switch lanes or otherwise make a traffic change without realizing that a motorcycle is near you.
It's that way with cars too. I was walking my dog down the street one night and I usually pay attention to approaching automobiles and get out of the way. There are no sidewalks in my neighborhood so I have to get off the road to let them by safely - usually by walking onto somebody's yard or driveway. However one early evening, when there was little light, one of those electric cars passed my by inches. I had no idea it was there until it was already alongside me and all I heard was a gentle "whoosh" as it went by. I don't think the driver even saw me. Almost got Stephen Kinged.
I have ridden and owned at least 50 different motorcycles of brands ranging from BSA to HD to everything Japanese. 90% of them cannot be heard from the front by people driving cars.
I’ll buy the complaint that pedestrians and bicyclists will be less likely to hear them. That holds water.
If you are in a car, you can’t hear my Goldwing, Zuma or Stella. You might hear my Panhead, but probably not, because you have your radio on.
In any case, a 20K bike that goes 60 miles is not going to sell. Even my Goldwing gets more than 42mpg. The cost of gas would have to go over $10 a gallon before electric bikes even become a consideration.