Because we have the technology now to represent that in real time, instead of just a dice roll. The ai should block, dodge, parry, or counter instead of us just missing. If we miss, that's because we fired the magic ball to far off course, or swung the sword from to far away. But if we're close enough and swing and visibly hit the target, and the ai doesn't block or anything then we should deal damage.
We had the technology to represent it then. :shrug:
Characters in Fallout would dodge if appropriate.
**Actually... It was possible in 1998 to have a fully 3d game that incorporated full melee combat with dismemberment and manual attacks (and blocking!); using weapons that dealt damage that was derived from how hard/fast you impacted on the target. The player could also have 100% control over their weapon, and swing it as they wished.
I wouldn't mind plausible [and detailed] reactions from NPCs that get attacked and/ or hit; NPC's that dodge, and even grapple.
As for missing due to "firing off course, or swinging out of range"... That is not the reason dice are used, and not something I would want in an RPG myself. Dice rolls used for attack and defense are to reflect the PC's attempt at the action. If you are playing a PC that cannot shoot straight, then he should not be hitting the target because you [the player] are good at aiming. The dice reflect the PC's best effort at attacking or defending. The same goes for Lock Picking (and other skills); the dice reflect their attempt ~and their attempt can fail, (but its usually weighted odds, and the better skilled they are, the less likely they will fail).