It was an IATA standard for 2 bags on flights to/from the US. I think most if not all have reduced the allowance at least for economy to 1 bag. This include AA, CO, DL, BA, AF, KL, VS etc.
In my opinion it is only fair as the standard allowance is 20kg for most airlines to most destinantions but was 46kg to the US. This seems to bring it more in line and make a more coherent policy.