Think of MTV. Stupid Boygroups are pushed because there is a majority of people who seem to like it. A computer DJ could produce the same effect. There are always enough people who want to hear the recent hit single of artist X again and again, or more generally spoken: The majority always wants the same kind of music.
So, a computer DJ might end up playing endlessly some OntheTop-Dancefloor-Trash or whatever the local audience might like. This kind of playing behaviour is actually happening in bad clubs with bad DJ's. - It is not with good DJ's, because they surprise and are innovative. You don't have to care about what the rest of the audience wants to listen to (as you might have to with a computer DJ) because you rely on the DJ, who makes his own unexpected choices.