What do you mean "still true?" The stereotype was never true.
There were Italian mobsters. There were also Irish mobsters, Jewish mobsters... There were mobsters of just about every major immigrant group in the US, especially if they were marginalized. Organized crime allowed these communities to not only build an economy of their own, but police themselves when they didn't trust the police.
The stereotype doesn't come from the fact that Italian mobsters existed, it comes from their portrayal in the media. The Godfather was popular, Al Capone was famous, so people got into it and made a ton of movies about Italian mobsters. That's all.