Actual source: fibular free flap reconstruction.

myoms.org/…/fibula-free-flap-reconstruction/

Tl;Dr the fibula doesn’t hold weight, it’s just there to provide a connection point for tissue and ligaments, so when you need a long, straight length of bone that isn’t doing anything important they just cut out a section of fibula. Plus if you get really really lucky (or are a child) it might even grow back.