The away goal rule was designed like that to minimize the chance of going into ET and if it however goes into ET to minimize the chance of penalties because:
a) Penalties are considered less fair 'cause it's a game of luck (as we know the game is considered a draw if it goes to penalties)
b) To not get pro players exhausted when they have to play 2 games a week (because IRL you just can't heal them with rest packs)

You just gotta deal with it or go watch CONCACAF CL