Much of the building design had to do with the existing site conditions, zoning restrictions, and client needs. To have maximized floor plates as the client desires, the elevator cores are pushed to the corners spaces available at the west end of the site. This permits the largest free open office space possible within the confines of the building envelope and site. The architect team has done their best to integrate these limitations into what I feel is an excellent overall design solution.
Original source: San Francisco Planning
By the way, those of you who think the Parcel F is the last of the so called "supertall" sites in San Francisco, there is still another 700 foot plus site just west of Oceanwide Center. It is that "U" or backwards "C" shaped site just above Oceanwide in the bottom panel of the three drawings images above. This is the Golden Gate University site. Plans for this site are still pending.