What I think is happening is that the government is cracking down on all kinds of smaller groups in anticipation for the big blow so that Nazis don't have an organisational base to fall back on. Much easier to behead a hydra when you kill the body first.

And while 150 people doesn't sound like much in this specific case that's only the adults, not the children getting indoctrinated, and it's also a very old (1951) group functioning as a corner stone of the wider scene. Frankly banning them was overdue but you can never rely on CDU and FDP to actually care.