I think that the two things that are the cause of this situation (or two of them, at least) are:
-In Europe, culture has mostly moved on: current Norse people are not vikings, current Germans are (mostly) not Nazis and so on, so it's easy to separate past grudges from current people; in the US, however, since when they fix things they either go back or they do't really fix the thing, the wounds of slavery have carried on to today, even if step by step they are being (very) slowly mended.
-Peple in the US are often under the impression that things outside have been exactly like how they've been there.
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I think that the two things that are the cause of this situation (or two of them, at least) are:
-In Europe, culture has mostly moved on: current Norse people are not vikings, current Germans are (mostly) not Nazis and so on, so it's easy to separate past grudges from current people; in the US, however, since when they fix things they either go back or they do't really fix the thing, the wounds of slavery have carried on to today, even if step by step they are being (very) slowly mended.
-Peple in the US are often under the impression that things outside have been exactly like how they've been there.