The resisters stopped the exodus from Buchenwald because, with the end at hand, they did not want to allow the Germans to massacre the Jews who remained in the camp.
Once the Germans knew that "it was all over", they began to transport large numbers of prisoners out of Buchenwald -
"April 2...rows of Jewish prisoners being marched out...perhaps to their immediate death, perhaps to other camps...On April 6, another 8,000 were marched out, non-Jews as well as Jews".
The purpose behind the exodus was to destroy evidence of German atrocities. The resisters at first did not rebel, because they were "not strong enough to fight them yet...there (were) three thousand guards (there)". At a clandestine Passover celebration on April 4 however, the resisters held seder and "chanted the Haggadah by heart". The service gave them "courage to try to survive (their) present suffering", and as the Allies approached and the SS tried to escape, they organized a rebellion to save those prisoners who remained (Chapter 14).