I think its music selection. At a wedding, you expect certain involvement from the musicians or dj for traditional moments, but constant shtick from either gets old. I've been to weddings where chest thumping music for the generation of the bride and groom only drove the aunts, uncles, friends of parents etc, home early. An average vocalist/musician/entertainer who has something for everybody trumps a better one who can't adapt to all of their audience. Of course you can't overlook that they have been previewed and selected for what they usually offer, then instructed what to play and paid for that. So its not always the performers error if everyone is not pleased.