I think it has to do more with fuel efficiencies and the airlines want to carry less fuel if possible by measuring all the bags and ensure not everyone is bringing their kitchen sink. It also has to do with what type of passengers they normally carry (that may violate the rules). Fuel price hasn't been at a rocket high these days so many non-US airlines have not came back on enforcing the rules. US airlines is all about if you can fit in the cabin then they don't care.

The rules are written there. If you did not get inspected, good for you. If you did, they told you ahead of time.