I have a property in the vicinity. If your trip takes you down SR 9B and not in the direction of any of those other locations, then the trip to a store not located along that trip is out of the way. For example, Beachwalk on 210 is another county. It's quicker to drive to several locations in Duval County if Publix is where you desire to go. If time and convenience is more important than the chain name, you end up going to a competitor.
As the area continues to rapidly grow, the opportunity for additional stores catering to the larger population creates itself. If it's not them, it will be the competition and then that's a potential market area they've lost out on. But make no doubt about it, no one is building a store that size and next to a full fledged interchange with the expectation that it is only to serve a limited captive audience. When E-Town is completed, you still won't have to drive through E-Town to reach that store at 9B. That interchange is set up to allow for commercial development that can also cater to the visibility and traffic created by SR 9B. If that were not important, Publix would be building in the middle of E-Town, far and away from immediate access and visual exposure to SR 9B traffic.
It will be no different from me getting coffee at Starbucks or gas from TA at the CR 210 interchange when driving to/from Central Florida. These places aren't necessarily opening to serve a specific subdivision or development. The market base they are setting up to cater to is much larger, at least that was the case when I worked on potential locations for their stores.
To bring this back to downtown Jacksonville, there's a reason McDonalds opened up on State and Union, instead of a random low volume intersection like Laura and Adams. There was a reason that Winn-Dixie moved from Ocean and Monroe to Union Street years ago. The higher volume streets allow for these businesses to access regional trips as well as the downtown market base. So if the DIA really wants to build a retail corridor effectively and efficiently, an important part of making that happen would be to look outside of the downtown silo and see how various corridors work regionally and take advantage of these market dynamics and site selection opportunities. There are numbers out there that can easily be obtained to support this, both in urban and suburban locations.