Just because your cheap home router does it doesn't mean it scales to thousands of users on one router. Some home routers are actually quite capable AND very unsaturated. I'm not trying to defend carriers but it is a very apples to oranges comparison.
We did that on low-end PC hardware 15 years ago for conference and guest networks (800+ simultaneous active users, LAN and WiFi).
I find it unlikely that Linux, FreeBSD have gotten less efficient since then and the hardware has made enormous improvements, far in advance of the common uplink speed.
