I remember reading “soy protein” (as a filler?) on labels when I was a kid. I’ve seen soy beans served in the shell at Japanese restaurants. Soy milk is readily available. I’ve even had Trader Joe’s chocolate-covered soy nuts.
But I’ve never seen soy beans served like… well, beans. Pinto beans, plack-eye peas, great northern white beans, kidney beans, lima beans… all are routinely prepared as something that can be spooned out and eaten with a fork. Ham hocks and soy beans? Soy bean chili? Refried soy beans? Pork’n’soy beans? Never heard of 'em
You can get soy beans in either dry or canned form. My Northeast Cooperatives pricelist offers several brands.
As to why they aren’t used in soups and such as commonly, I really don’t know. WAG: they are small and not highly flavored and are traditionally passed over for other varieties. Or, the fact that they are easily ground into paste (for making tofu) suggests that they might tend to fall apart while cooking.
The Book of Tofu by William Shurtleff and Akiko Aoyagi gives a few recipes for using soybeans in stews and salads, but they do seem to be traditionally processed in various ways.
They are quite often served as beans in Japan. They look unremarkable, but I think they taste rather good. They don’t fall apart during cooking all all that easily. You can even get roasted soy beans - looks like peanuts and have very similar texture too. Another popular dish is “edamame” (4 syllables), which is soy beans harvested while they are still green. They look exactly like peas, but have a more nutty flavour. Wonderful when steamed still in the husk and lightly salted. (You don’t heat the husk, you pop the beans into your mouth.)
I’d guess Americans (and europeans?) don’t commonly eat them as beans because they think of it as cheap food, not worthy of being a dish by itself. Come to think of it, wheat is usually not used as whole grains either. Same reason
You can buy whole soy beans (Edamame) at Trader Joes or most grocery stores. But they are cheaper at Trader Joe’s. Anyhow you just boil them whole, salt the heck out of them, let them cool in the fridge or the freezer if you are in a hurry and suck them out of their shells. Uhm, yummy. That actually is about the only way that I like my soy.