What if Disney bought Viacom?

Instead of The Walt Disney Company buying 21st Century Fox, why doesn't it buy the rights to ViacomCBS?

Media
Disney will own ViacomCBS' various companies and networks.

Film studios that will be owned by Disney

 * Paramount Pictures
 * Nickelodeon Movies
 * Insurge Pictures
 * Paramount Animation
 * Paramount Players

Television channels and studios that will be owned by Disney

 * Paramount Channel
 * Paramount Network
 * Paramount Kids
 * Paramount Television Animation
 * Nickelodeon Productions
 * Nickelodeon Animation Studio
 * MTV
 * MTV 2
 * MTV Tr3S
 * MTV Music
 * BET
 * BET Soul
 * BET Jam
 * Nick At Night
 * VH1
 * Comedy Central