An excellent point! People are unwilling to die for a lie. This was shown abundantly well with the death of Hitler where the day after there were no Nazis in Germany or after the fall of the Soviets where nowadays there are no Communists.
My two bits ...
They died for David Koresh and Jim Jones. Not only that, but they killed their own children. Of course, in the case of DK, they might have rationally expected the government not to behave like a two-year-old having a tantrum. (But I suspect many of them knew what would happen).