One problem here is conflating the copyright and the license (the "public license"). Basically, every piece of text created in the US is copyrighted. Even if you want to give away your work, it is under your copyright and you allow re-use under a license. That's how Creative Commons works. That's how free and open source software works.
The legal system is NOT set up for simply releasing work into the public domain. See, for example, https://creativecommons.org/about/cc0
"Dedicating works to the public domain is difficult if not impossible for those wanting to contribute their works for public use before applicable copyright or database protection terms expire. Few if any jurisdictions have a process for doing so easily and reliably. Laws vary from jurisdiction to jurisdiction as to what rights are automatically granted and how and when they expire or may be voluntarily relinquished. More challenging yet, many legal systems effectively prohibit any attempt by these owners to surrender rights automatically conferred by law, particularly moral rights, even when the author wishing to do so is well informed and resolute about doing so and contributing their work to the public domain."
Establishing copyright and providing a permissive license is the way these things are properly done. The ONLY problem with how the Common Core is *licensed* is the stipulation that reproduction is permissible only "for purposes that support the Common Core State Standards Initiative."
What this means is that under the license I could produce "Tom's Common Core Standards" (since "Common Core Standards" is not a trademark). As long as I provided attribution for the standards I directly copied from the CCSSI Common Core, I could mix in my own standards or modified standards as I saw fit.
If the NGA and/or CCSSO decided that this use did not constitute "purposes that support the Common Core State Standards Initiative," they could charge me with breach of the license for that reason. If that went to court, it could probably go either way, especially if my version emphasized that its purpose was to propose improvements to the Common Core and to strengthen its mission.
Even if my publication of "Tom's Common Core" was found to be not supporting the CCSSI, I would still have a strong fair use argument, assuming I wasn't selling my version. My standards would be primarily non-profit and educational in purpose; standards by nature are usually based in part on existing standards, and NGA and CCSSI have no direct commercial interest in the standards.
Finally, the license is clear that current, not-in-breach licensees (users, readers) cannot have the terms of the license retrospectively changed. NGA and CCSSI could sell the copyright, they or someone else could issue the standards under a different, additional license, but they can't take away the license that has already been granted to reproduce the work, in whole or in part.
The Common Core process is controlled by the rules in Race to the Top and other federal guidelines, and by the tests. Those are sufficient for their needs.