Every American kitchen has measuring cups, few have scales. And people learn that method and continue to use it (most people don't even know about zeroing a scale after you add each ingredient).
It may also be that US measuring cups are "more convenient" sizes than the equivalent metric ones would be.
For flour, they often specify "sifted" which removes some of the variability.
> Every American kitchen has measuring cups, few have scales.
There's no reason Americans can't buy scales.
I got mine for $15 at Costco 10+ years ago. You can still get them from Amazon or Walmart for less than that.
> It may also be that US measuring cups are "more convenient" sizes than the equivalent metric ones would be.
When measuring out flour, I don't use a measuring cup at all. I put a bowl on my scale, hit the Tare button to zero it out, then add whatever number of grams of flour I need to the bowl.
> For flour, they often specify "sifted" which removes some of the variability.
That's gotta be awkward to sift into a measuring cup.
The reason is momentum. Switching to measuring flour by weight will require households to have both measuring cups and scales, require recipes to be rewritten, require cooks with an intuition based on volume to relearn the intuition based on weight. None of this is insurmountable, just like none of the reasons for switching from imperial to metric are insurmountable, but for people getting things done, it's not enough of an issue to worth making the switch, so this kind of switch would require an institution or coalition with enough clout to make the switch and pull everyone else along. For cooking, I don't believe such an institution or coalition exists.
The problem is recipe book authors want to sell to all Americans (especially that group that always buys recipe books but never actually uses them) and so they aim at the widest possible market.
Brings to mind a convo about coffee a few years back. A friend was quite surprised I owned a scale accurate to the tenth of a gram just for dosing coffee beans when I could just use a super accurate scoop instead. I left it at that, and didn’t go into how I account for humidity affecting grinder retention, etc.
It may also be that US measuring cups are "more convenient" sizes than the equivalent metric ones would be.
For flour, they often specify "sifted" which removes some of the variability.