
That’s because rape is significantly harder to prove than murder is. It sucks but that’s just how it is. I agree that in situations like you described the killing should be charged more lightly but lowering the standards for a murder to be considered “justified” would be an extremely damaging thing to do.
Rape isn't necessarily harder to prove. Rape kits routinely never get checked by police and are left to rot on the shelf. Folks who report being raped are ignored or ruled against because of what they were wearing or how they behaved. Evidence is left at every crime, and evidence in rape cases is intentionally ignored