The best explanation for why the influence of the U.S. Constitution and Bill of Rights has lessened in recent decades is:
The U.S. Bill of Rights, while revolutionary when it was written, increasingly seems too limited in comparison to newer rights documents.
This response suggests that as societal values and understandings of rights have evolved, many newer constitutions and rights documents have encompassed a broader range of rights than those originally outlined in the U.S. Bill of Rights, making the latter seem less comprehensive or relevant in current contexts.