You seem to be making two points, one I wholeheartedly agree with and one I don't.I think that everything in this thread is totally wrong. Many people that read this forum have bought bikes from reputable sources in good faith, and your scaring them into not using them because they'll now be thinking that they're illegal when they're not - just like that poor guy with the scooter. It started with a premise that has never been tested in law, and until it is there's little to worry about. Even if your bike doesn't comply with EN15194, you've got more chance of winning the lottery jackpot than being prosecuted for having an illegal bike. We should be encouraging people onto ebikes, not scaring them off them.
In the meantime, I'll carry on riding and enjoying mine.
Firstly, uninformed customers have a moral right to know whether the product they are buying is legal to use. I think it is morally reprehensible for a vendor to sell a product that doesn't meet the required EU or UK regulatory requirements WITHOUT making that clear to the customer.
Secondly, I share your view that the probability of getting caught, or having been caught then being charged, is miniscule, provided that the ebike you are riding complies with the spirit of the regulations.
However, the two are completely separate issues. An informed customer can choose to buy and ride an ebike that hasn't been shown to meet the regulations, so they are taking that very small risk of getting caught willingly. An uninformed customer will be taking that very small risk unwittingly, and it could end up shattering their life if something untoward happened.