There are at least two reasons for this.
First, the values of Europe and the US have grown apart. The US is more aggressively capitalistic than most European countries. It is more religious. It favors guns and the death penalty. All of these things seem wrong to many Europeans.
Second, the Cold War has ended. With the end of the Cold War, Europeans need America much less than they once did. They no longer need to be protected from communism.
So, Europeans and Americans' values have grown apart while Europeans have stopped needing America as much as they once did.