RF channels actually are a finite resource on a coax segment because the aggregate capacity of one port coming off the CMTS is considerably less than properly implemented singlemode fiber. Because most residential customer traffic is inbound, like people watching netflix or browsing the web, they allocate the capacity asymmetrically.

https://volpefirm.com/downstream-channel-bonding/

https://volpefirm.com/docsis3-tutorial-introduction/