People will assimilate only if they feel they need to. In Europe, Muslims don't think they need to.
I'd thought the Greeks got rid of any residual Moslem populations in the 1920s but I guess not.
BTW, personally I find most Greeks and most Turks who live in cities, or near the Aegean to be pretty much alike as far as culture, behavior, etc. are concerned. It's like they are the same people divided only by language and religion!