Consider devices like the HTC One, or any of Sony's recent Xperia flagships, or the Moto X with its wood and leather options. These are gadgets with decades of engineering inside of them, but which have nonetheless been painstakingly designed to look gorgeous on the outside. And nothing spoils that quite like a big honkin' FCC-required ID and safety label hiding on the metal finish. Manufacturers can try to make it blend into the phone's default color, or hide it behind a battery cover or on a bezel.
So, technically using software to unlock digital carrier blocks on your phone in the US is a violation of everyone's favorite draconian copyright legislation, the Digital Millennium Copyright Act. Unlocking your phone yourself could be seen as breaking a "technical measure," akin to cracking a DRM package (which, in most cases, is illegal). The Library of Congress can grant specific exemptions, like it already does for rooting and jailbreaking, but the latest one in 2012 was passed over without renewal.
In October of 2012, the Library of Congress elected not to renew DMCA exemptions that explicitly allow end users to unlock their cell phones at will, thus ending a six year tradition. This has made a lot of people very angry and has been widely regarded as a bad move. The quest to do something about it began almost immediately. And by "almost immediately" I mean "nearly three months later and at almost the very last minute."
Still, regardless of when the outrage gained steam, the fact is it did.