There is a history here of vehicles being sold to the public being regulated. But there is also a whole industry of aftermarket companies selling modifications, with lobbyists and attorneys to represent them and their users. Once you own a vehicle you can generally do whatever you like with it. I've seen some of the Ebike, and Emoto vendors showing up at the trade association's annual show. SEMA (Specialty Equipment Manufacturers Association). There is some question as to whether it's illegal for me to modify my own bike or not. Cars it's definitely not a problem.
To put this in perspective, I'm a retired truck mechanic. I was required to hold a license to drive the vehicles I was working on. Up to 80,000# GVW and unlimited HP engine. Typically 425-500HP. It's actually kind of amusing to see all of the EU and the Britsih Isles getting upset over someone riding a 2HP bicycle????