The problem is that the price you (as the ISP) choose to charge some new startup is not subject to competition. That's because you're not charging your custome

The problem is that the price you (as the ISP) choose to charge some new startup is not subject to competition. That's because you're not charging your customers. You're selling them to that startup. The startup has no choice but to pay if they want to have a chance of reaching these potential customers. That means ISPs will have to ability to milk every cent of value generated out of startups, limited only by their ability to measure it. The normal mechanisms of a market don't kick in, because the customers will be unaware of what's happening. They're not going to change providers only because that provider is shaking down some startup they've never heard of.