With more groups active - there was quite a number of faaaar left polical activists advocating armed rebellion etc.etc, but most were communist idealist romantics - the security service would have had to act earlier on the robbery preceding the Købmagergade robbery if because of anything - lack of resources!
You can just follow so many groups at one time and Danish police/security service wasn't geared to that.
BTW the Wiki article label makes it look like the biker/street gang gunning down each other these days - Blekingegade certainly wasn't. It just show the difficulty in transforming the meaning of the word from one language to another.