They addressed this in the section entitled "Problematic cases of IP address fingerprinting"
By using IP as the ban id they created a system that constantly and regularly banned completely innocent steam IDs, thinking they are somehow linked when a new steam id uses a banned IP, which is nonsense. They just did not notice because the banned gamers did not complain.
So if the same connection(plug in wall) can end up with IPs from different blocks, well, trying to do anything sensible with this is too complicated.
I remember this being hilarious when idiots would ip ban me back on the IRC days: "oh no, I have to press the reconnect button!"
Which seems to have been best practice for IPv4 and is still best practice with IPv6 :
https://www.ripe.net/publications/docs/ripe-690/#5--end-user...