There is no reason a creator cannot continue doing what they want to do. Look around you at the artists/creators that pretty much only do cars, or bedrooms, baby stuff, wedding gowns (and the list goes on. No one should tell any creator that they have done 'enough' of one thing. Many, many creators have 'themes' or such that interest them or they want to do for their sims and share with us.
If you don't want Harry Potter things, just do not download them.
