Speedruns and records. For my guild in particular, the point of playing is to own the game as much as possible and to beat all competition on both this server and other servers. Disabling world buffs puts us at a great disadvantage compared to guilds from other servers. For example, we would like to do a proper world buffed Naxxramas speedrun before K1 dies, but we need world buffs for that to be competitive and in order to completely beat the competition by a large margin.
Some people here may not care about what I described, but it is very important to us. No need to even mention that it promotes Kronos and brings players to the realm when you have high performing guilds.