But nevertheless, books are not limited to artistic endeavors. Plenty of books offer inventive ideas and are protected by copyright alone.
Right. Well, it's not my assessment. It's the assessment of Congress that has enacted the relevant copyright statutes, and the judges that have written relevant case law opinions.
"Plenty of books offer inventive ideas and are protected by copyright alone"
A book has no functionality other than the function of communicating words, language. The code contained inside software actually does something - That "something" is what is inventive.