Probably in the same way that one could explain how the existence of Taco Bell does not preclude racism towards Mexicans.
American Chinese food is a lot sweeter, thicker, and more soy sauce based.
Your equivalent statement about Mexican food would be that you assume Taco Bell is what most Americans are eating as Mexican food. That doesn’t seem a valid assumption at all - maybe for a certain demographic (e.g. young) that’s true, but I’m very skeptical that such a claim would stand up to scrutiny.
Similarly, you cannot group the corner store (nominally) Chinese restaurant owned by a Chinese (or as likely in much of US, Korean) family as being in the class of highly processed, pre-made food as Taco Bell. Sorry but no.
In China, 味精, "essence of flavor".
Non-instant ramen is also essentially salt + oil + glutamate flavoring + noodles.
If you like you can take instant ramen and add a soft-boiled egg, some vegetables, and some fatty pork, or whatever other set of toppings you prefer.
Not sure what noodles to source, tho.
And for slightly more goodness, Asian marts will generally carry ready made broths and alkaline noodles. And one can whip up a broth from box stock if one wants something better.
Pretty much the same reason why Americans think it's bad for health. It has a scary-sounding name (it's also called "MSG" in Korea), it sounds like a "chemical", and you can find it in ingredient lists of all popular junk foods - most notably instant ramen, which is basically an MSG+salt solution masquerading as noodles.
Give something in food an exotic name, and people will invent reason to fear it, like all those people demanding gluten-free bread.
Besides, if "racism" is the explanation behind it, how are you going to explain the immense popularity of Chinese food everywhere in America?