"In modern airliners, the primary advantage of FBW is that it allows engineers to use lighter wing and tail structures"
Why?
My answer:
Simply because electrical wires weigh much less than mechanical cables ... that is the primary advantage ! ... but there are many other important features which allow FBW to be chosen by manufacturers (i.e. computers fit better with FBW than traditional flight controls and have a lower cost).
Best Regards,
captain87