It would significantly increase the amount of work. There are currently 671 articles in at least one category. Every single one of these would have to be edited to be put in a beta category, and then again to be put in their final category. If we don't take this approach, only some of these 671 articles will need to be edited, as not all categories will be renamed. This would require only a few hundred edits instead of over 1300. I don't know about you, but I have better things to do than making 1000 extra edits to trial a new structure.