the focus of those shows you mention is not about murder but crime solving drama. therein lies the appeal i guess. a dead body with loads of clues and a dramatic or twisty sub plot adds the entertainment. a straightforward bank robbery would make it feel like keystone cops, and rape - although it is dealt with in some quarters - would make for uncomfortable emotional viewing, rather than bland dead person/catch killer (with the aid of the worlds most amazing computer software of course).
most people watch the shows saying 'i knew it was him/her' or 'humph, that computer just took a piece of toenail and pinpointed the exact location of a mass murdrer in a dockside warehouse downtown just seconds before he killed the leading incidental character, that aint real'. they don't watch it and go, 'aw poor person got shot/stabbed/blown up' etc etc becuase we know it aint real.