From the drawing, the tower is in the middle of the structure. Only one span of the bridge was set in place. The suspension cables couldn’t be put in place until the opposing span was in place.
I don’t know how they thought the bridge span could be left in place unsupported in the interim.
The opposing span was shorter and over water
Suspension tower should go in first
Opposing span second
Then the (now collapsed) span
Attaching cables, tensioning,
Then removing hydraulic supports