Original: One could hypothesize that some ideological fanatics might systematically revert, or eliminate, changes made only under the CC-BY-SA license to their favorite articles, so that they remain available under an incompatible license.
Simplified: One could hypothesize that some ideological fanatics might systematically revert, or eliminate, changes made only under the GFDL to their favorite articles, so that they remain available under an incompatible license.