Lots of e-bikes use fat tires because it offers extra stability and comfort. Since lots of e-bikes already weigh a fair amount the additional weight of the tires is not as big of a concern. On top of that, the motor helps offset the tire weight so the benefit of comfort and stability really shines through. Due to the numerous e-bikes with fat tire options, the trend has sustained and it seems the average e-bike purchaser is interested in wide tires.