Some of it has to do with the anniversary of Toei animation a few years ago. I was in Tokyo for that, and Toei did a lot of promotions between DBZ and One Piece to celebrate their success. In addition, the creator of One Piece, grew up as a DBZ fan, and he has made it mission to help this generation of kids become fans of DBZ by linking it with the current success of One Piece as the #1 anime in Japan. Then even did a cross over with the two animes at one of the anime conventions and a small manga called "Cross Epoch". The lead character Luffy is based on many of the character traits of Goku, and the series has a similar comedic edge to it being a fighting anime like DBZ. There's even One Piece DBZ crossover statues that you can buy where Goku is wearing Luffy's outfit and vice versa. I bought the Goku figure in Japan then; it's an awesome pose.
For this movie they even did an early bird ticket fans could buy in Dec that featured both Goku and Luffy on the ticket, and it was a combo ticket for both "Battle of Gods" and also the One Piece movie "One Piece Z".
So with all my rambling.......Toei Animation is trying to keep the DBZ franchise alive by weaving into the success of One Piece with the help of the One Piece creator, Eichiro Oda. These are some of the factors why we have seen an uptick of DBZ resourcing.
Hope they keep it up! As a matter of fact, that's why they are hopefully continuing DBZ Kai into the Buu saga. The Japanese govt is actually providing much of the funding to create Kai after it had ended a few years ago. They claim that it is funds to help further the culture of Japanese entertainment or something like that. Sounds to me more like the govt officials are grown up fans wanting to see the next saga!
