It seems the retroflex d and t are present in some Germanic languages but not in most Romance, Slavic, and other IE languages.
I know that it occurs in IE languages of Asia, like Sanskrit, Pashto, and north Indian languages, (but not Persian), which could be explained as contact with people having these sounds in their language, but my focus is specifically on Europe.
Has there been any explanation given why it occurs in Germanic but not others?
PS: I am a rank amateur in linguistics, so I have used "some" and 'most' just to be on safer side.
EDIT: I am a bit embarrassed that I mistook the alveolar stops t and d to be the retroflex ones; to me they sounded the same. It appears that only Norwegian and Swedish have them, as opposed to English, German and Dutch that I had listed in the original question. However, this information won't affect my interest in the topic. I have updated the question accordingly.