However, any scoot or bike with an engine displacement of less than 400 is not allowed on our freeways...
Why? How fast do you usually ride on your freeways?
No matter which modern 400cc scooter, they all can exeed 140kph.
That's enough for every American or European country, incl. the German Autobahn (partially unlimited, you may ride 400kph or more if you can).
(Not to mention an old (198x) Suzuki RG 400 with 4 cylinders 2stroke and a top speed beyond 200kph.)
I know from a similar old rule in Italy: >150cc.
Had the effect, that the 151cc bikes used simple carbureted engines with low rpm producing less power output than the modern fuel injected 125cc. Actually nobody cares about the displacement. It's a relict from ancient times (i.e. 1946 Vespa 98cc and 60kph, 1948 Vespa 125cc and 70kph).