Musicians who write modern music are only considered successful if many copies of their songs are purchased, so part of their writing contains a hook. This is a technical term for a set of musical notes or a phrase that is repeated during a piece, and it is primarily a way to catch the attention of the listener. For musicians, it is their connection to popularity. Listeners often find this phrase a drawing point within a particular song, so they want to continue hearing it and singing along.
Few songs today are written without a hook, and many people who produce music demand there be one within any piece. For them, it is a selling point that will reap profits. The musicians, with their need to create popular music, see it as a way to further their career while creating their own following. Those who will play or sing the music find it is a good way to increase their connection with a specific audience, so they are also interested in having a good hook within the song.