2 National Monument Land Reduced by 'over' 1.1 million acres

Just as wild guess, but it may be possible that an act created in 1976 does not cover national parks, designated as such, after 1976... just those in existence at the time the act was signed.

Since the parks being reduced were declared national monuments by 42 and 44 (not so long ago) it is safe to assume the declaration and the reduction are both political.