Mobile service in the US is handled by a small group of providers that are an effective oligopoly. They bundle services including voice, text messaging and a connection to the Internet (and a few others). These are marketed in bundles, the components of which do not necessarily directly relate to the cost of providing the service. Over time the components of the larger bundle are shifted around to reflect the current state of marketing.
Text messaging, by itself, is enormously profitable. But people value it and pay what seems like a huge amount of money given the amount of data exchanged (over $1,000 per megabyte in some cases), but the pricing is an artificial number and just one of the components of the bucket. It is possible to avoid most or all of your carrier's text messages by using Apple's iMessage service, WhatApp, or any of a number of free services that use the Internet connection of the phone for the link.
Some of these third party messaging apps are much more flexible than conventional text messaging and in some parts of the world are becoming common. As they become more common in the US, rest assured the carriers will readjust the bundles in their offered service plans to preserve their profits.
WhatsApp is interesting as it caught Firms like Facebook sleeping. Facebook didn't offer a competing service, while WhatsApp has grown to nearly a quarter of a billion mobile users in a few years - capturing users Facebook and others would have loved to have.
We'll be moving into more of a world where voice is carried over the Internet and the need for regular phone service will begin to fade. The carriers will make an adjustment for that too. It is too bad you can't buy individual services - just as it is too bad you can't unbundle your cable service. These marketing devices exist to protect some very high profits and, rest assured, if unbundling was forced, the component prices would be very high - largely due to nature of oligopoly. I'd be in favor of making carriers offer nothing but an Internet connection and a conventional dial tone service -- but to make that work you'd need real competiion and the bar for doing that is too expensive in infrastructure as well as in Congress. (although some work-arounds are emerging) Part of the problem is artifical $pectrum $carcity and there are ways around that with time and some change of thinking among the regulators. I'm not terribly optimistic.
In the meantime you can enjoy a bit of arbitrage and ditch your text messaging plan.