you can shout that all you want but it does not make sense.
Armor Class is made up of so many abstract concepts that there are plenty of times that it doesn't make sense for a "miss" to hit someone else in melee combat.
High AC could mean that you are really good at dodging.
It could also mean that you are wearing thick metal armor that makes arrows bounce off.
If you shoot someone with an arrow, and it hits their armor, goes "plink" and falls to the ground, it doesn't make any sense to allow that "miss" to damage someone else standing next to the target.
If I'm really good at dodging, and I duck under your arrow, why doesn't it have a chance to hit the guy standing 10 feet on the other side of me, but it does have a chance of hitting the guy standing 5 feet to my left?
Three reasons firing into melee simply imposes an attack penalty instead of a complicated "maybe you hit your friend" rule are:
1) AC and attack rolls are so abstract that trying to make them model realistic physics is silly.
2) "Miss" means something very different than "my arrow didn't go where I aimed it"
3) Hitting allies with attacks isn't fun.