The big ISPs install fiber where there are a lot of customers (lower cost per customer) and try to sell their triple play packages, internet, phone, and TV, with upgrades like HBO.
Comcast's Triple Play of cable, Internet and digital voice has three tiers based on the features that a customer may want priced at $130, $160, and $200.
If we assume most customers come chose a low tier, or don't get all three services, we can conservatively estimate $125 / month average (some customers get the deluxe sports package and HBO and
So why do munis have so much trouble paying off their capital spend? Munis tend to do put more fiber in less densely populated areas, increasing their capital cost per customer. They may not offer the same service packages, with premium TV channels and such. Instead, they may focus on internet, leaving customers to pay Netflix,is Hulu, Amazon, etc for the content. That reduces their average revenue per customer even if the customer is spending more overall by purchasing content from other companies.