I've always been fascinated by how disgusting the bread is in the US. Do we know what lead to this ?
Greed. There's no simpler explanation. It starts with trying to find bread-like material that tastes even better. You can do so by adding sugar. You want it to last even longer on the shelves so you make it non-perishable with chemicals that weren't previously used in food that are just grandfathered as "safe" to appease industry. Thus you get US Bread.
If the US is the outlier the question should be what condition that are US specific made it happen, not a general concept like greed.