If they didn't peer with anyone they'd be a closed network and it would be illegal to advertise that as "internet access". They're legally required to live up

If they didn't peer with anyone they'd be a closed network and it would be illegal to advertise that as "internet access". They're legally required to live up to the claims of their product. If they say X Mbit/s then there needs to be at least a plausible case made that they can achieve those results. Anything significantly less is to invite a class-action lawsuit.