I think it's because immigrants who came to the US could not find equivalent ingredients to their traditional recipes as easily. Also distribution of fresh food

I think it's because immigrants who came to the US could not find equivalent ingredients to their traditional recipes as easily. Also distribution of fresh food is hard as you go west. So people had to settle with low quality recipes and food. This resulted in there not being as much of a food culture in the general population. So now nobody (as in the average person doesn't) cares about how food tastes like in the US.