"What's the point of paying $100 a month for Facebook and Instagram? I get that on my phone anyway! I don't want Verizon's $100 a month TV plan, I want house of cards."
As the ISP mostly has sunk costs and slim margins if even 5% of its user base leaves in a certain market that will render them insolvent or force them to raise prices, causing more departures, and higher prices still...
The point is while they don't always have direct competition they do have a decent amount of elasticity of demand.