Well most Americans want to see something back for their brilliant ideas.
Say you are a scientist and you've spent 15-20 years in a lab everyday, exposed to horrible chemicals, and studying, reading, researching, and suddenly you find the cure to cancer. In a democracy you are paid off for your hard work, while in a communist society, the government is taking your idea, and reproducing it, and you still work in a lab as a scientist and never see anything for you accomplishment.
Now there are pros and cons to this. You discovered the cure for cancer, so guess how much the cancer patients are spending to buy your patented one-of-a-kind no-other-competition medications? Probably an arm and a leg, in the metaphoric sense. Communism wouldnt have that problem.
But if making these discoveries dont change or improve your situation, are you still going to spend time going above and beyond to make great discoveries and invent great things, even with no reward for it?
There is the ideal of the "American Dream", which is to make money, own a home, a job, and family, and therefore me happy. Americans will work extra hard to invent and discover because in the end it all pays off.