Probably because there aren't enough people in Greenland to get a good riot going. Shakespeare wrote about riots in England--some of them, to be sure, targeted against Germans. Scotland has had its riots, Berlin has had some. I could mention the Boston Tea Party, but let's face it, those Yankees were immigrants.
The Yankees were colonizers more than immigrants --England had dominion over the territory and people came over to colonize as English subjects. In other words they were 'domestic' immigrants as opposed to alien (Swiss, Spanish, etc.) immigrants.
Why do countries which didn't have unsafe streets now do after immigration?