The word suicide is used because in a suicide by cop scenario, the individual makes it clear, typically in some written manifesto, that his/her intention is to commit suicide because s/he doesn't have the means or courage to do so otherwise; some also want to die with the fact that they'll receive attention after death, as crazy as that is. You seem to believe that a suicide can only occur when someone is isolated in a room and cuts, shoots, hangs him/herself, etc., which isn't the case. By your claims, there's no such thing as say suicide by train either.