Funny as a patent is granted for much less time. You’d think patents and copyright would have the same duration
Or, in other words: a patent can block access to something that is potentially irreplaceable, and that would have been discovered by others, eventually. Donald Duck just wouldn’t exist without Disney.
The goal of copyright is to provide some incentive for creation. At the same time, it limits the distribution of those works and the benefit that brings, an effect called deadweight loss. Those two goals—amount & quality of creation and distribution—are in perpetual conflict, and the limited time is supposed to balance them for maximum benefit. Is death + 70/95 years too long? Yes, defjnitely. I remember seeing something like 15 years being floated as the true optimum, but it’s likely to differ by category. But it’s just as annoying to often see complete ignorance or denial of the basic mechanism (I. e. “Commercial music suxx anyway” or “why should I pay for news”)
(Another item on this scale: trademarks, which are entirely imbued with value by the owner’s exclusive right to use them. They are not time-limited as long as they are used because, to a first approximation, the value of “Levi’s” has nothing to do with the beauty of the word (which one could consider a limited ressource), but depends on the company’s interest in maintaining its status)
After subscribing to Disney Plus I immediately began to notice their use of a segment of Steamboat Willie in place of a static or simply animated trademark. It seems clear to me what Disney's strategy will be going forth: to get as far they can abusing so-called "motion marks" (i.e. animated trademark symbols) to re-capture as much of their expiring copyrighted content they can.
However far they get--it will likely take decades for the dust to settle after years of intensely testing the legal waters and lobbying Congress for various tweaks--I don't doubt that it will prove very effective. Trademarks can in principal provide protection in perpetuity, as you say. Motion marks let you significantly expand the scope of the mark (and art), so you can protect a broader array of merchandise as well as films--not much market for public domain copies if segments have to be removed. Plus with their army of lawyers they can widen that moat even more through sheer intimidation, so they may very well be able to squash alot of otherwise highly marketable derivative works.