It's that way for the same reason that Majority Toughness is used in rolling To Wound as well as other simplifications, because it saves a ton of time doing Wound Allocation over doing everything 'correctly'. We've had editions where Wound Allocation could take 10-30 mins just to work out who died, especially with people trying to take full advantage of the various ways of making things more complicated to keep important models alive/spread the damage equally over multi-wound models and keep them all alive.
Every game i've done up until that one followed the idea that you do the wounds to all models under the blast and take em out that way. For instance if a small blast hit 6 models and the wound rolls does all 4 wounds then to determine who actually gets killed we'd assign a number for each model 1-6 varying upon that as needed and roll a d6 for each wound and that number means that model died. 4 is a heavy flamer so that guy is now dead, 5 was a Sargent so he takes it (not including look out sir etc) 2 being a normal troop unit and 6 being a pysker for example that way its not like you said being bullshit where people try to make it so only the ones they don't want to die stay alive while the others don't.
I mean i can understand how some people can be absolute 100% assholes with wound allocations and that shit but most of the guys i've played with have been pretty chill and got their own way of getting around that kinda stuff without scream fests on what hits what, what wounds what and what dies.
Be warned he who looks not where he walks for he may find himself facing death itself.