Yeah that is a good question. I can only assume they had more guns in the truck, but left it all there when they ran.
While I enjoyed most of the scenes with Joel and Ellie, I really didn't care for anything else. We already have David coming up, not even to mention the final act... I don't see why we had to dedicate screentime to new villains. In this case, the hunters in the game were good enough. What Joel and Ellie learn about them in their travels was all the information the audience needed - they overthrew Fedra at the QZ and now are ambushing/robbing from trespassers in order to survive.