First of all, it is absolutely not accurate to say that the Jews did not fight back against the Nazis and the Holocaust. In fact, they did engage in many acts of resistance. Perhaps the best known act of resistance was the uprising in the Warsaw ghetto. This uprising occurred in 1943. It happened when rumors circulated that the Germans were going to clear the ghetto and send everyone to a concentration camp. There were many other episodes of armed resistance. Many Jews joined resistance fighters, particularly in the parts of the Soviet Union that Germany had conquered. Therefore, it is simply wrong to say that the Jews did not fight back.
As for why more Jews did not fight back, there can be many answers to this. One answer is that it is often very difficult for people to believe that something terrible is going to happen to them. When the deportations started, it would surely have been hard for Jews to believe that the Germans would actually try to kill that many people. As what was happening became clearer, individuals might have held out hope that somehow they would be saved (and, obviously, there were a relatively large number who did survive the Holocaust).
A second answer is that it would have been exceedingly difficult to fight back in any meaningful way. It would be very hard for any group of people to try to fight back against a trained army. It would have been even more difficult in the circumstances of Nazi Germany where the Jews had few supporters who could help them get weapons, ammunition, food, and other things they would need for a rebellion.
Thus, it is wrong to say the Jews did not resist, and it is easy to understand why they did not resist more.
Again, the Jews did fight back. In the ghetto in Warsaw, they fought back, but sadly, out of the 445,000 Jews there, only 100 escaped.
In Europe, thee Jews were either fighting back or protecting their family's from certain death. Also, they didn't know they were going to die, no one did. All people thought was that they were going off to work in Eastern Europe and were told that the gas chambers were shower blocks. They were unaware of the fact they were most likely going to die, but fought back, if they could and if they ever found out about their death.