That whole scenario was plot. If you look at what's currently happening in the manga, you can see that Naruto is already OP. Kishimoto's plan has always been to make Naruto and Sasuke equal, but that can't happen if Naruto had all of Kurama sealed within him. Naruto having all of Kurama sealed within him would actually make him almost invincible.
I know this all sounds weird, but I think that's why he could only seal half of Kurama within Naruto. Many reasons have been given about why Minato was never able to seal Kurama completely, but all that was most likely said to help the plot.
This is my reason on it.