The cellular industry, due to its high barriers to entry (stemming from the enormous initial infrastructure costs), tends towards a natural monopoly. In this case, it hasn't quite reached a monopoly - instead, we have 4 main companies (AT&T, Verizon, Sprint, and T-Mobile), also known as an oligopoly. I know there are smaller carriers, but since they don't provide coverage everywhere, their product is not the same as the one provided by the 4 major carriers.
The problem is that when there is a disparity between the value of a product to the buyer and the cost of production to a seller, if there is natural competition (cereal, gasoline, etc. are relatively close to natural competition), the actual price will tend towards the cost for the sellers, since companies will keep undercutting each other until the price drops to the lowest they can accept without losing money on each sale. OTOH, if there is a natural monopoly (or something close to it), the actual price will tend towards the value for the buyers, since the lack of competition allows the price to rise as high as the buyer will tolerate.
In the case of bandwidth, the marginal cost for the telecom companies for each byte transferred is miniscule compared to the value it provides to us. If we had an industry with natural competition (like they do in other countries where the government owns the pipes and the telecom companies simply lease it out), then we would only be paying that miniscule cost (which essentially rounds off to a flat monthly fee for unlimited access). But since we have an industry that tends towards a natural monopoly, the companies will milk us for every penny we're willing to give them.