User blog comment:SeaTerror/Abolishment of the Shichibukai System/@comment-137.154.49.133-20140219023818

I think it is not just Isshou that wanted to overthrow the shichibukai. I think the marines want control of the whole world. The marineford was relocated to the new world to challenge the Yonko and the marines according to Jimbei back in the fishman island arc was way powerful than they were before.

I think the reason why the World Government established the shichibukai because the marines are not strong enough to beat the Yonkou. Since the marine is getting more powerful and probably become more confident to challenge the Yonko, they wouldn't need the shichibukai.