Actually, I'm not sure developer Forest City Ratner really wanted the convention to come to the Barclays Center (where, at the time the DNC was under consideration, the developer was selling tis 55% share of the operating company). After all, it would have shut down construction of Greenland Forest City Partners' Pacific Park Brooklyn project.
Because they couldn't have had project-related trucks idling outside the arena, blocking traffic on Sixth Avenue, as shown in the Instagram and video below from Wayne Bailey. Note the quote overheard from the driver: he didn't know where to go.
2016-07-26 815am again a @pacificparkbk 18 wheeler tractor trailer stages & blocks traffic on 6th Ave bet Dean & Pacific until finally workers tell him to move (full video YouTube username AYInfoNYC) #empirestatedevelopmentcorp #aycdc #nypd78thprecinct #pacificparkbk I could hear the driver yell "no one knows where I'm to go" watch the video