In other words, why isn't MS13 infiltrating Norway, if there's no competition for their illegal activities?
In the United States, for instance, there's a huge market for gang formation, and gangs thrive despite constant fighting for territory.
[0]: https://www.ssb.no/en/sosiale-forhold-og-kriminalitet/artikl... (mostly in Norwegian, but some parts in English)
I never claimed immigrants are somehow intrinsically more disposed to crime. In fact, the report doesn't make that claim either. It shows that crime rates vary greatly based on where immigrants/refugees come from.
It's not simple, there are many causes of such a effect. But offering free education and other opportunities that are substantially better than crimes is a good guess.