After defeating the Death Troopers, they discovered that the cargo was actually a giant kyber crystal that would be used to power a certain weapon.
Ezra and Sabine wanted to prioritize getting the workers to safety, but Saw’s mission was not about rescuing some civilians.
Unfortunately for them, the cargo was being guarded by a bunch of Death Troopers, which was an immediate sign that something very valuable was on board.
The trio left Chopper to take care of the workers while they went after the mysterious cargo.