Does not require the reader to write anything (e.g., practice problems) or do anything beyond just reading and thinking, except perhaps on very rare occasions.

You should drop this criterion, because it excludes recreational mathematics books, such as those by Martin Gardner (who is perhaps the most famous popularizer of mathematics). Most popular mathematics and popular science books seem to cover history of mathematics and science and biographies of mathematicians and scientists and pay much less attention to mathematics and science themselves. Thus recreational mathematics books are better example of what I think should be classified as popular mathematics. Besides recreational mathematics, an example of a popular author whose books are about science (rather than scientists) is Yakov Perelman, though his books are quite old.