Sure, though I don't know how much helmets were relevant, there is also the not-so-trifling issue of the 2 stroke and many older Euro level engines having been

Sure, though I don't know how much helmets were relevant, there is also the not-so-trifling issue of the 2 stroke and many older Euro level engines having been de facto progressively forbidden, some complications for getting driving licenses, the (debatable whether justified or not) resistance/fear of parents in letting 14 years old drive into the traffic. In the '70's and '80's (AFAICR less so in the '90's), any kid was waiting to get 14 to be able to get (if the parents could afford it) a moped, even a Ciao, and then started waiting to get 16 to be able to get the "A" driving license and be able to drive a 125 cc. I think that there has been a general shift due to these and possibly other factors that made mopeds (but also motorcycles) less desirable to most young people.