Because the market itself cannot provide decent competition. Even if you got rid of most regulations, you'd still have barriers in the forms of having to tear up roads, and the massive investment in equipment you have to buy up front. That would still keep other players to a minimum. Net Neutrality is there to ensure that we still have the internet as we know it even if most people don't have competition between providers.

Because non promotes completion, not hinder it. Not all regulations are bad.