How come T20 Traveller didn't do this?
T20 did do this, you may want to re-read the armor rules in T20, they are radically different from any d20 based game, and make more sense than the normal rules. They make a lot of sense when you think about them from an advanced tech point of view, that's why a human has a chance of surviving a fusion gun blasé f they are wearing combat armor or battle dress.