Personally I look at throttles as a safety feature. I'm only familiar with my own bike (Rad Rover) so I don't know if this is true of all Ebikes. If I have to come to a stop in 6th or 7th gear on any kind of upward slope it is extremely difficult to get rolling again without a throttle. I only tried to once while on a bike trail where my throttle was unplugged to comply with the "only class 1 allowed" rule. I was on an upward slope and tried to get going in 6th gear (only shortly after owning the bike) lost my balance , tipped over, and lost about a quarter inch patch of skin on my arm. In hind sight I should have turned around to go downhill and lower my gears and then turn around again. These days the only time I use the throttle is to get rolling from a dead stop but I'm still glad I have one.Not sure if any ebike rises to the level of being overly complex but I do tend to favor simplicity. I have yet to ride any pedelec / pedal-assist with the array of sensors (torque, speed, cadence, heart rate, etc.) that provides the desired assist under all riding situations. I do think they provide a more traditional bike riding experience but the simplicity of throttle-assist just makes more sense since the rider then is always in complete control of the level of assist. Sorry programmers, I just think I know what assist I want better than any algorithm you can develop for an ebike.
That said, the federal definition written by a PhD Electrical Engineer is more elegant than what the spandexters at People for Bikes came up on the 3-class system. It makes no sense at all to have separate classes for pedal-assist and throttle-assist with everything else being equal. I will also argue that not allowing throttles on Class 3 is just bizarre when they are in most cases being use regulated to streets and road side bike lanes where every other vehicle they are moving with has a throttle / pedal. There was no reason that the "simple" federal definition of a LSEB as a bike was not better for the industry but People for Bikes got lobby money and they did what Bosch wanted.