Why can't you fully unlock stuff through single-player?

[GabeFan]

Originally Posted by Yossarian

I know it means you can't fly a few aircraft but other than quickly trying it out in training mode they serve no real purpose except online.

I LOVE playing in training mode, so to me there would be a purpose. I'm not much of a multiplayer guy, so it would be nice to have ALL the planes unlockable in single player mode.