America only entered WWII to take a piece of the pie.

It was pretty clear at that point that if the US didn't enter, the USSR would take the win and have the chance to bring more Nazi-occupied territories into their union. Many US corporations were even collaborating with the Nazis, the US made carve outs to prevent factories in Nazi territories being bombed, as we already know the US profits immensely from war, and then after the war they shipped all the Nazi scientists and generals into high places in government. They weren't exactly sworn enemies. Defeating the Nazis was not as high a priority as limiting the influence of the USSR. Their participation was always cynical, which might be why it seemed "counter-productive" at times.