Stylized gun play is well within Hollywood's realm, haven't you seen the Matrix or Wanted? That's easy for them and CB has far less cross cultural issues then DB. Heck not only is stylized gun play within Hollywood's realm its within their comfort zone.
DB has stuff that is way out of Hollywood's realm and comfort zone. First its based on Journey into the West, a story not a lot of westerns are familiar with and it deals with things that are hard to translate to screen, like planets blowing up, super ultra transformations and ultra stylized kung fu fights.
CB is way more Hollywood friendly then DB.
Now you asked why are these films are being made, its simple, the studios are trying to make money, they want a pre-established story with an existing fan movement, so there is a greater of chance of success, in their minRAB.
Ultimately its up the Manga companies to decide what do with franchises, they can ignore Hollywood and thus ignore the dump trucks of money Hollywood can bring to their house, I'm not sure that's likely, I would assume most of them like money. They just sign over the rights and let the studios do whatever they want, ensuring a high likehood of a bunch of really crappy movies based on Manga, until Hollywood simplely loses interest or they can take a creative interest in these movies and try ensure they are somewhat faithful and as well as good. It is also the responsbility of the Manga companies to ensure thier characters are treated right by hollywood.