Why are sink-mounted garbage disposal units usually banned in Europe but allowed in the US?
Part One: valid reasons
Different communities will  have built different sewage treatment facilities, with different design load capacities. There are newer communities in various spots in the USA which actually require food waste to be Dispos-al-ed, as this cuts down on edible waste in dumps (reducing gas emission and vermin population). Their treatment facilities were built with capacity in mind. Other communities, or older regions, do not have such capacity and need to minimize the amount of solid waste in the sewer system.
Part Two  actual reasons
Sadly,  many laws and regulations get passed with the best of intentions, and 5or 10 or 50 years later the world has changed.  Getting a legislature to review and fix old laws is almost as difficult as getting quarks to exist as solo particles.