What are these wiggly USB 3 traces on my motherboard?
My best hypothesis is that these are common mode noise filters

The thick regions in each section represent capacitors, most likely to the ground plane of the pcb.

The half loop pattern in the middle would seem to be a common mode choke for really high frequency noise. USB 3.0 runs in the gigahertz so this seems about right. The common mode choke is a classic approach to reducing noise common to both sides of a balanced line while having little effect on the differential signal that is desired.

Together these form a CLC filter called a balanced PI filter network.