We all benefit from the knowledge and the creation in some way, but the creator enjoys additional substance in exchange for his efforts. Our forefathers did indeed use the words “limited time” in these matters. Well, time is naturally limited to that point when the Creator folds things into something new. Anyway, I question our forefathers as to why they thought it necessary, and how strongly they felt about this limitation. It is something we are free to hash out. It is also something - like anything - that is subject to excesses in either direction. To me it seems commercial success ought to play into how long a given creation is allowed copyright protection.
I agree but have hesitations at part of your last statement. It should not be just commercial interests that determine copyright, although they should play a part, and they have played a part in the recent extensions of copyright term. The advances to the author and the enormous cost involved in producing a book have warranted some increase in the term of copyright. No more literary tea party. The money people took over a while back.