The nice thing about keyboard accompaniment is the ability to easily alternate between inversions of the same chord to provide a more interest sound. On the guitar it means shifting your hand position up or down the neck a lot and can leave things sounding quite choppy (for most of us of less than virtuoso status). Plus some inversions, particularly those with the 3rd in the bass don't sound so harmonic on the guitar. The overtones in the bass strings can get out of hand.