Obvious troll is obvious, but I’ll feed you and say it’s because –
1- You still have to be fit to ride them. You can’t go with no fitness, they are still a bike, it is still hard to get uphill. You just have some help.
2- They won’t go any faster downhill, the assistance stops when you reach downhill speeds (15mph ish).
3- Most walkers won’t be able to tell the difference.
4- They have such low power they won’t make any more erosion.
5- They are assisted, not out and out motorised. You have to work for the motor to work. Which isn’t the same as a motorised vehicle.
And a myriad more reasons. I suggest you go away, do some research, have a go on one and realise that they are actually not an issue at all and go worry about something else.