Why is there only one save file in Pokemon?

I don't think anybody would have an answer to that other then NIntendo. I was always questioning myself about that too. Maybe in Japan (Nintendo is Japanese) they can't have more then one save files on there game. That's a great question you have. It might also be because they want it to be like it actually is starting over Pokemon in real life. If you want to start over you pretty much have to let go all your pokemon. Hope this helps!

I don't really. Maybe its a memory thing with the card or nintendo wants us to play pokemon right. If you feel like starting over the game but don't want to lose your pokemon and items(I'm assuming this from your question), just trade it over to another game(a friend's game who you could trust)and get back weak pokemon so neither of you really lose anything. And then, when you restart, just trade it back.

If this question was just out of curiosity, then that's the same for me. But nowadays, I don't start new games. I just stick with what I got.