I'm not up on NYC code, since I don't live in the city, but I wonder if it was a rebuild of an existing wooden tank under a "repair in kind" exemption. I have seen shit like that before, such as codes that allow knocking down all but one wall of a building and still calling it a "remodel" (and thus preserving grandfathered code exemptions).

I interpreted "using" in the context of construction methods, since it was attached to the material, not the object like your statement is here. To me, your statement implied that new towers are still being built with wood. It sounds like you meant to ask why wooden towers are still in use.