To give a serious answer, you are paying for infrastructure. Most ISPs build infrastructure to your home and you pay to use it, but they are still paying a Tier 1 provider access to the backbone. It would not only be extremely, very specially costly for someone to build a private use ISP, it would also probably (speculation here) not comply with FCC regulations.

Not to mention, even if you went the extra mile, and paid for all the equipment to be your OWN Tier 1 backbone provider, you would also be paying peering fees to the other Tier 1’s out there.

The INTERnet, is a group of providers, not just one. Huge ISPs like Comcast could not function without the others, despite their peering agreements.

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