I can't understand why they are put through - any dancing school in the land could submit a group just as good (or as bad, depending on which way you look at it!). They never get voted through, I think viewers just can't be bothered with them.
I'm wondering if the judges have to work to a quota system, e.g. so many dance troupes, so many magic acts, etc. just to give the show the variety aspect that it's supposed to have. (People are already complaining about too many singers, I suppose they have to pad out the show with other acts.) I bet there would be a row if no dance troupes at all were put through, you just can't win in situations like this.