As I/O speeds increase, issues of signal integrity and power budgeting create new challenges.
Simply put, high-speed signals are harder to manage than low-speed signals.
The higher the interconnection speed, the more difficult it is to manage return loss, insertion loss, crosstalk, and similar factors that can degrade signals.
While an ideal cabling system would have no intermediate connections between boxes, the real-world need for production breaks and modularity necessitates connectors in the path.
via Copper and fiber co-exist in commercial aerospace – Intelligent Aerospace.