There are three new pro dancers this year, so they have changed it a bit. As for changing the rest, I'm not a particular fan of any of the names you mentioned, but I still don't think it would be a great idea. They all have fans, and that brings in viewers.
Also you sometimes notice with new pros that they take a while before their choreography hits the right balance between being demanding for the celeb and being enjoyable to watch. So it probably does the show a favour that the majority of pros each year have done at least one previous series.