Survival of the Fittest
It highlights just how resilient these creatures are. A cockroach can live for a week without its head (it only dies because it can’t drink water). They can hold their breath for 40 minutes. They can survive nuclear fallout radiation levels that would kill a human instantly. We are fighting an enemy designed for apocalypse survival.
Stepping on them is a brute force attack against an enemy designed to survive physical trauma. Their exoskeletons are flexible plates, not brittle shells. Sometimes, “crushing” them only stuns them or compresses them into a floor crack, allowing them to recover and limp away later. Unless you hear a distinct, wet *pop*, you might not have even finished the job.