excess baggage

One of the things I didn't realize when we came here, and the main reason it's so hard to pack now, is the airlines treat you differently when you're American.
Actually, to be exact, they treat you differently when you're traveling to or from the US. When we came here, we were each allowed to check two bags. They could weigh a total of something like 75 kilograms, or a number almost as large.
Now that we're leaving, and we're not flying directly to the States, the numbers change. We're allowed to check one bag each. It can't weigh more than 20 kilograms.
We came over with one large backpack, one suitcase and some carry-on bags. Each. Now we have to sort all that stuff, along with everything we've acquired in the past year, into the one bag of 20 kilos for the next four months; what's worth paying a hefty fee to ship home; and what we're willing to get rid of.
It's a pain for us at this point in time. It's a perk I'm going to use happily in the future, I'm sure. But it also makes me curious as to how the discrepancy came about: I don't think we pay any more in airfares for the privilege of carrying more luggage. Is it just the airlines are more worried about upsetting Americans who can't carry every worldly possession than they are about upsetting any other nationality? Do we rate more highly on the airlines' service list since we spend more money? Is it a grand social experiment? Or are the airlines just giving into the reality that Americans have more crap, are more attached to it and put up more of a fuss if they can't have it? That's probably it - we get to carry more luggage so the airlines avoid having to deal with our tantrums.