The reason is primarily culinary taste.
Yes, it is completely true that American-Chinese cooking is considered by most Chinese to be its own style of cooking, completely separate from traditional Chinese cooking.
Most Chinese prefer the taste of salt, and don't like overly oily foods, meaning that they generally don't eat very sweet dishes, or too much fried dishes.
Chinese restaurants in America however, cater specifically to popular American taste, which they believe is primarily sugar and oil. All of the most well-known Chinese-American dishes that people buy are either very sweet or fried.
Sweet and sour chicken, check.
General Tso's chicken, check
Chicken fingers, fried
Crab rangoons (love these), friend dumplings with cream cheese for filling, hmm, you figure out the math.
Even the vegetable dishes are made with a much sweeter version of sauce than the Chinese eat themselves. ie, basic stir fry seasoning for regular Chinese home cooking is usually just soy sauce, ginger, garlic, cooking wine, salt... but the version Chinese restaurants use adds a heapful of sugar and corn starch often is used too for thickness.
It's not that they put the meat on different parts of their bodies, the Chinese have a different preference than most Americans when it comes to eating, they don't really dig sugar and oil that much, they prefer salty food more.