Steve you are not a singer, so I do not expect you to understand. unfortunately singers are not always able to sing in a concert situation where there are no distractions.
I remember years ago being booked at a festival and the venue was acceptable, however there was an open door in to another room, where there was a television on and a tennis match was very visible from the performing stage, to aid concentration the only answer was to sing with eyes shut, however if the performer interacts with the audience whilst introducing the song, a good performer/ audience relationship can be established, so that closing eyes during the song is not in any way detrimental to performance.