What if Disney bought Viacom?

Instead of Walt Disney Company buying 21st Century Fox (if the deal falls), then why doesn't it buy the rights to Viacom?

Media
Disney will own Viacom's various companies and networks.

Film studios that will be owned by Disney

 * Paramount Pictures
 * Nickelodeon Movies
 * Insurge Pictures
 * Paramount Animation
 * MTV Films

Television channels and studios that will be owned by Disney

 * MTV Original Productions
 * Paramount Network
 * Paramount Kids
 * Paramount Television Animation
 * Nickelodeon Productions
 * Nickelodeon Animation Studio