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.
Regarding music, I was talking about music being inventive or not, not some legal definition. Being “inventive” does not require that it have physical utility.