They don't let you save at the end of most Zelda games (
OOS and
OOA being the exceptions) because after the end theres nothing to do. You would just be wandering around, fighting a couple enemies here and there, talking to people who are now happy and hoppy and thanking you and you walk around some more, maybe find a heart piece but theres really no point because all of the hard enemies are dead, walk some more, hum dee hum. And just imagine what it would be like saving at the end of
LA. You get to sit there and float. Yay. If you saved at the end of
OoT, you could only be a kid, and it would still be boring. Perhaps if they put in little tiny sub quests at the end of the game, but then you still couldn't beat the boss again so you would have to go through the whole game to do that, and so on.