Residential ISPs don’t work financially unless you oversell peak time full-rate bandwidth. If you do things right, you oversell at a level that your customers don’t actually slow down. Even today, you won’t have 100% of customers using 100% of their full line rate 100% of the time.

Back in the late 1990s we could run a couple dozen 56k lines on a 1.544 Mbps backhaul. We could have those to the same extent today, but there’s still a ratio that works fine.