Well, that's why there are terminator games, in which the aim is to kill individual opponents. The aim in standard is to win the game. Often, in flat rate or no cards, this aim is best achieved by sitting back and letting an opponent kill off players for you.
In escalating, a player who kills a number of opponents but does not win the game will often have either mis-calculated mid-turn cashes or the number of armies required to win.
In either case, rewarding the player who has done the dirty work for the eventual winner would result in rewarding poor or illogical play that is not well-suited to the ultimate aim of winning.
I see no need for this option with terminator games already in existence. In fact you do not explain how your suggestion differs to terminator games. As far as I can tell you are proposing that we abolish standard games
