Why? Because he can, that is why... He takes advantage of a legal loophole that let him makes movies when they flop (which most do, considering their quality). He is "the producers" of german film industry.
The question of wheter it will actually be good is something else entirely. Boll is a troll, both on his comments and on his work (the statement that he will aim to make a better holocaust film that Schindler's List is yet another proof of that). He is most confortable being a troll, as when he aims to be political, shocking or controversial without any real merit (just watch Postal... or, better yet, don't watch Postal)... there is nothing in his career that makes me believe he can pull this off with any kind of sensibility.