Angrygumball has a good point, it is weak storytelling to keep these teams together, but RyougaZell isn't too far off either.

These are A or S rank missions, going up against Akatsuki S-class villains, so you're not going to see any rookie Genin or even Chuunin in these episodes, even if more Genins and Chuunins have graduated or been promoted in Konoha. Besides, why would Kishimoto introduce even more characters when the current batch is already so under-utilized?