This ! power of friendship ...Because he doesn't want to. He wan'ts to keep them all separate to preserve their personalities/names.
This ^^^^.You need Gedo Mazo for that to work, Naruto only has the beasts.
Also that's counter productive, the idea is that Naruto is going to guide the tailed beasts down the right path, he can't do that with the Ten Tails because it isn't intelligent.