It's boring for me. Prayerful, beautiful church singing consists of more than just getting the notes right. Perhaps you already know the notes. But a robot can sing the right notes. There are a lot of other things which are worked on in rehearsals besides the notes.
Most choirs have a fair amount of turnover.
This means there are always people who are just learning the tones and the music. These new people need help in order to learn. One of the most valuable things a choir director can have, in trying to teach the music to new people, is the presence of at least one knowledgeable person in each of the four parts. This can only happen through rehearsal. There is a large body of music repertoire available, which many choir directors would like to introduce but cannot because of a lack of attendance at rehearsals.