What if Comcast buys Viacom?

Since Disney won a bidding war for 21st Century Fox, why can't Comcast buy Viacom (except for the 50% of Paramount Pictures) from National Amusements instead?

Media
After Comcast's acquisition of Viacom for a NBCUniversal-Viacom merger, NBCUniversal will own Viacom's various companies and networks.

Film studios that will be owned by NBCUniversal

 * Paramount Pictures
 * Nickelodeon Movies
 * Insurge Pictures
 * Paramount Animation
 * MTV Films
 * United International Pictures (50%)

Television channels and studios that will be owned by NBCUniversal

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