I always thought the show dance was the last dance?

It was until this year. It's a shame really - I quite liked the aspect of the anything goes routine being the last chance to win votes and the competition.

Agree 100%.

I wonder if they have decided its so bad most years that they don't want to end with something weak.

They have too little time to rehearse or devise anything that good and more and more of the obvious musical routines have been used either as showdances or series dances.