Why does Andrew Watt play so much guitar on the album?

According to the credits of Foreign Tongues, Andrew Watt plays guitar on 8 of the 14 tracks. The Rolling Stones are a band with 2 guitarists, and Mick also has guitar credits on over half the tracks. And Robert Smith contributes guitar to another track as well. When a band has this many guitarists, why would the producer need to contribute any guitar at all?