The point of a CDN, at least a significant one, is to reduce latency. To put your content closer to your customers. It also lets you handle larger load, is more resilient to DDOS, etc, but, at least in my view, those are often secondary... the main issue is latency, and perhaps capacity.

Gigabit to your house won't remove latency, other than perhaps to apps hosted by google (including google, obviously)