Sure they are. Plenty of film and streaming projects are based on older work. Sapkowski's Witcher series comes to mind. If his rights to the IP had expired after 20 years then not only would Netflix been able to rip his work off for free, but he wouldn't have benefitted at all from the resurgence in popularity that his novels garnered. It would've just been gravy for some publishing company -- how would that be fair?
I do think that the current copyright regime is too long. I guess I'd like to see something like ~25 years from publication for human authors, but easily/cheaply renewable to lifetime copyright; and 25 years from creation for copyright held by companies, or for works for which the copyright has been assigned to someone else other than the original author, with no renewal.