That’s the problem with a monopoly/oligopoly situation — profit is not maximized by maximizing revenue. A cable company may get better growth by lowering rates, but they will lose profits. Meanwhile, growth in and of itself is meaningless to them since the whole point of grwoth is to gain so much market concentration that you can raise prices — they already have the market concentration and high prices.

The only way to lower cable prices without diminishing the quality of the service offering would be to forcibly introduce more competition. Since the high infrastructure deployment costs make this a natural monopoly situation, the only way to force more competition would be to force structural separation — network operator and service provider cannot be the same company. This way, you might only have one or two network operators per market, but they would be wholesale and there would be numerous retail service providers for consumers to choose from. This was what the Telecommunications Act of 1996 was supposed to do, but it was completely sabotaged by incumbent resistance and very effective lobbying.