baggage restrictions in North/South America

Passengers on flights to/from/having a stopover in the U.S., Canada, and “certain” South American countries are limited to two checked bags at 32 kg each, while passengers on all other flights are limited to 20kg of checked luggage TOTAL. This seems to be true in general - I checked Cathay, Qantas, BA, and Lufthansa, and their websites all say this. I even called Cathay to verify, but customer service could not tell me why. So, when I fly from London to L.A., I am allowed (more than) three times the luggage than when I fly London to Hong Kong. Is there some sort of law in the U.S., Canada, and “certain” South American countries (a list of which I could not find)? There must be. But why? To protect us from unfair baggage limitations? To ensure that airlines don’t carry too
much other cargo? What’s up?

There was a thread about this a few weeks ago…it seems the answer is simply that two different standards have arisen separately from one another, one for transatlantic services, and another for all others. There’s no way airlines will ever agree to carry 32kg on all flights, and it would be difficult for them to try to reduce the limit on transatlantic services. So we’re stuck with this contradiction.

Here is a link to the earlier thread.