Right, but then customers are going to be either really disappointed at that number or the price is going to skyrocket when basically every internet package becomes dedicated.
Under your rule there would really be no way to sell 'best effort, capped at X' internet packages.
You can oversell by quite a lot and still meet an advertised speed with 90 or 95% reliability.
If you want to sell 'best effort, no promises' then don't make promises. Or promise something low, like "2mbps" or "2-20mbps".
The real disappointment comes when you can't reach the advertised speed for multiple hours every day. There is much less disappointment in the end if the advertised speed matches a state of moderate, everyday congestion.
Under your rule there would really be no way to sell 'best effort, capped at X' internet packages.