I think an important thing to remember in this game, and it's something I think about every time the dice don't go my way, is that you the player are almost never in command of a competent force, you are playing a mob of unorganized junkies incapable of any true discipline. Even when you factor in a faction like the palanite enforcers, it comes with the caveat that your cops frequently take bribes, sell their spare clips of ammunition for booze money, and occasionally fall off of ledges because they got shot at, panicked, and dove for cover at a height measured in stories.
You are correct that in a situation where your heavy stubber gets jammed, the tactical response would be to have other fighters, cover the weapon while an engineer moves in to support, but this is Necromunda, where the event of "Greasy" Raf jamming the heavy stubber because he took a hit of obscura and messed up his bursts of fire is met with jeers as every idiot fighter on the field thinks they can sort this firefight themselves. No one comes to Greasy's aid, and even if they did, Greasy would not let them touch his beloved heavy stubber, which he won in high-stakes poker game.