Three reasons:
1. No concept of fighting back, for most.
2. Careful work by the nazies to create an impression that cooperation = safety, if with inconveniences
3. Concern about "making things worse" for family members.
Knowing what we know, we can reliably say that those who use threats are likely to carry them out regardless of our degree of cooperation.
Question to the folks here, though: if a police officer is about to arrest you, do you fight there and then or do you hope for the best and ask for legal representation? And if the latter choice is true, how different are we from those Jews? The difference seems to be that our police is mostly lawful whereas the German (Soviet, Polish, etc.) weren't. But our own behavior seems similar: we prefer uncertainty of the official justice to the uncertainty of an immediate firefight. If the police/paramailtaries are lawful, we do well, if they aren't, we get Waco.
Valaam Shalamov wrote a story called "The Last Battle of Major Pugachev" which dealt with one of the two major uprisings in the gulars (both in 1946, I think). Both started by ex-military who were imprisoned for either just seeing the West or for being POWs. Both failed. The one Shalamov described (and I couldn't translate it, the officalize Russian is pretty much Newspeak for the purposes of rendering it in English) had about a dozen participant and they were eventually hunted down. The other uprising involved a take-over of a camp and that was no match for snipers and infantry supported by tanks...the authorities could pick and choose when to move.
As John Ross' character said: "It is too late when you are behind wire and eighty pounds underweight." Anyone who would try to render another person unable to fight inthe future is that person's enemy. If the attempt to disarm is unlawful, the perpetrator should be killed, both to safeguard the would-be victim and to deter others from trying to do the same.
To re-state the old question: is an SS typist as culpuble as the E-Grouppe triggerman? Yes. Triggerman comes first (safeguard), typist comes next (deterrent). No prisoners. The wages of sig should be death, and I can't think of any sin worse than initiation of violence against an innocent. FWIW, I don't think that any functionary wearing the uniform of an organization like Gestapo or its modern equivalent is innocent, even if they don't do their own killings.