I can think of two reasons why this might be so slow, though have no insider info.
One, high interest rates mean construction loans for future phases of construction might be desirably delayed.
Two, they (dev) is hoping they will have to give back funds held by unit holders, so they can resell when economic and market conditions are stronger.
Perhaps I am being too creative here, and its just sheer incompetency, but why would this site have more issues (putting aside ingress and egress) than next door, or any other site for that matter with a multiple tower build occurring?