Mirrors on both bars
As I've mentioned in the comments, I've got mirrors on a couple of my bikes: a Zefal Spin on the tourer and a Busch &amp; Müller Cyclestar on the hybrid.  Both are convex, and cover a wide area, and both mount on the end of the bars. They're very useful, though mainly for keeping up awareness of the situation. The B&amp;M in particular sits quite far out and covers the lane I'm in as well as to the side where cars overtake (I'm in the UK where we ride on the left, but I'll try to make my description ambidextrous). On the rare occasions when I commute on my MTB, without a mirror, I really miss them. 

But while there are cases when traffic can be coming up from behind on either side, such as when lanes split to go in different directions, you don't just need to see what's behind and to the side, you need to scan everywhere, and be seen to do so. I've also ridden in France, without moving my mirror across. I didn't find it very helpful at all having a mirror on the kerb side of my bike, even when there was traffic to that side. I'm not on an e-bike, but when I just need awareness of traffic on both sides, I'm often going faster than e-bikes legally can (here, under motor power). 

Another reason: A mirror on the near (kerb) side isn't used nearly as much as on the offside; in fact they weren't required to be fitted to cars in the UK until much later. I don't ride a motorbike, but do drive a car, and there the main reason to use the mirror on the kerb side is to check before pulling in after overtaking someone, especially on a multi-lane road. You don't overtake very often on a bike, except other bikes, and everything is slower and closer together than when motor vehicles overtake each other - there's plenty of time to turn your head and check you've passed safely.