Yeah 49cc mopeds that aren't registered appear to still be a thing where I am (Boston). And I think it's 49cc 2-stroke so equivalent to like a 90cc 4-stroke (whether that ends up violating a different emissions rules, I don't know).

Still, parking is such a racket in Seaport, including unnecessarily strict ticketing on motorcycles, that I don't blame the delivery guys for using the mopeds. I'm not sure what their realistic alternative would be.