The lack of competition is the actual reason. When Google was entering markets with their Internet service suddenly incumbents got capacity to provide competitive speed at slightly lower price. Essentially causing Google to give up with that initiative. If a company with "unlimited" amount of money like Google can't enter to compete, no one can.

And if there is no competition, you no longer charge competitive prices, you charge what people are willing to pay. The whole promotional plans they offer are used to figure out how much you are likely to pay. Once the promotion expires and you don't call to get it extended, you are basically saying that you're ok with increase. Once enough people don't do that, the price will go up.