They're putting up the easiest sections first, and leaving spaces open to make the site generally more accessible. For instance, the second support tower for the top hat would impede a lot of the work area they need for putting in the surrounding themeing, so they buried the footers to allow cranes and vehicles to move about more easily. Once they finish the lagoon wall in that area and get the remainder of the s-bend up, then we'll see the top hat be completed. I'm willing to bet come this Friday, the helix will be done.