Because who doesn't like to have his or her own anything-concierge.
Sometimes you just want a musical playlist that fits the moment, through either the correct mood or activity. It is less about your personal favourites and more about matching the context.
There are huge record stored organised by genre and artist, where you go to your various corners of interest and scan through titles and find what you want. And then there is the personal shopping assistant; you walk in the door and he simply asks: what do you need the music for?