In theory, yes, and I think most people here would store their backup codes properly. However, there are many people who don't store them properly, and don't think about it until it's too late. They lose their token, break their phone, or lose access in one of the many other ways.

Sure, you can say "tough luck", but then people will complain, reasonable or not, and Google probably doesn't want that to happen. I think this is a reasonable compromise when it comes to security and usability.