Quote: "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."
Yes, from about seven years ago up to thirty years ago the standard checked baggage allowance for economy class to and from North America was two pieces, each to not exceed 70 lbs. 70 lbs was the maximum weight the baggage handlers were allowed to lift. (The same maximum weight applied to mail bags in the UK in the 1960s.) Carry-on bags were in addition to this. This allowance applied to all connecting flights elsewhere that were part of the same journey; e.g. on a ticket from Durban, South Africa to Thunder Bay, Canada SAA had to provide this allowance for the flight from Durban to Johannesburg, BA or SAA then had to provide it between Johannesburg and London, BA or Air Canada had to provide it between London and Toronto and Air Canada or Canadian Airlines had to provide it from Toronto to Thunder Bay.
Mrs. C and I regularly flew between South Africa and Canada, the UK and Canada and Canada and elsewhere in Africa and always received this allowance for many years. It worked fine for some decades so there is no valid reason why it should not still apply. The answer is to not just reintroduce it to and from North America but to extend it to all other international flights.
PS: Remember that this was a maximum allowance. Many passengers, including us, often were well short of the maximum limit.