Telecoms have huge marketing budgets. A large portion is just a zero-sum war with competitors (another portion is enticing people to upgrade existing service).
Those are effectively a source of hidden profit margins--NFL, Major League Baseball, et. al. get them instead of the telecom operators, but when looking at how much prices could drop, you have to consider that.
Telecom service is by its very nature a high-churn business: you lose approximately 20% of your customers every year. Churn happens for a lot of reasons: people move, competitors offer better deals, or people simply get rid of the service (but the "people move" one is actually probably the biggest). But because it's a high-churn business, you have to do brand marketing so that when people say "I need TV service. Who offers that?" your name is the first one they think of. Since so many of your customers leave you (and your competitors) every year, you have to be constantly acquiring new customers through a variety of means. If you don't, you'll be out of business in 5 years flat.
The huge marketing budgets don't go away if you suddenly split the market between a dozen or so providers. In fact, overall marketing spend across the industry would probably go up substantially because there would be more competition for limited consumer mindshare.
Total bullshit. People don't replace the wires in their yard every 5 years. Sure, they move (and immediately get replaced by new customers), and they sometimes opt out of the TV service and increasingly opt out of landline phone service, but the only "churn" that's relevant to this discussion is people switching between DSL and Cable, which wouldn't matter if we could get one set of neutral cables installed to get the data to and from the nearest peering points. The rest of the churn you listed and its overhead costs are for the parts of the business that need to be divorced from the actual internet connectivity.
If you have multiple ISPs selling connectivity over a carrier-neutral set of wires, they're going to be trying to poach each others' customers whenever they churn. Any business with high customer churn carries high marketing costs because the return on marketing is relatively good with 20% of the market up for grabs every year. With more players doing marketing in a zero-sum system, overall marketing spend is likely to rise, not decline.
All I'm saying is that the marketing costs wouldn't go away even if the big cable companies do: they would just be replaced by a dozen smaller companies doing the marketing, billing and connectivity. These smaller ISPs would just be taking each others' customers rather than customers jumping ship to DSL or some other last-mile tech.
Those are effectively a source of hidden profit margins--NFL, Major League Baseball, et. al. get them instead of the telecom operators, but when looking at how much prices could drop, you have to consider that.