There's no reason to not have front motor drive on a bike.
Some may object to how the added weight affects steering, but it's far less than using front b panniers which are common enough to challenge that objection.
As to motorcycles, the answer is obvious. Non-electric front wheel drive is problematic because there's no easy way to get power from a motor to a front wheel.
The reality is that there are design advantages to rear wheel drive E-bikes if starting from a blank page. OTOH there are significant front wheel drive advantages in terms of cost and simplicity, if adapting a pedal bike to E-bike.
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