Disney is making movies out of public domain stories because it's easier without the licensing overhead. Same is true for songs. Elvis and the Beatles fade because their songs cannot be shared without learning about the licensing agreements. A fate that Dylan could have avoided.
The Beatles followed the Disney/Nintendo school of copyright management, where you just hold onto something valuable for the fear that actually making money off the thing you own will make it worth less in the future. This is what gives you shit like the "Disney Vault" where you periodically take old works off the market entirely for the sake of artificial scarcity. In this particular case, The Beatles were a massive hole in pretty much every digital music store's back catalog, so much so that them finally selling digital copies of their songs was considered actual tech news.
Whether or not a work actually thrives once it's been escheated to the public domain is really complicated. You see, the act of reusing something in the public domain also grants you copyright over anything you added to the work. Disney's reuse of public domain stories not only saved them money, but it also took things out of the public domain, in a sense. Yes, all of the old Hans Christen Andersen stories are very much open to reuse, but only if you're careful not to use the bits Disney added into their adaptations - and there are a lot of them. So if your goal is to just keep the work accessible and relevant, something akin to a Creative Commons ShareAlike license might be more appropriate than a public domain dedication.
I don't know, sitting on one's catalog until digital music storefronts are widely established and you've been holding out long enough that the eventual release is a newsworthy event seems like a perfectly reasonable marketing decision if you ask me, typical back-catalog revenue numbers being what they are.
In the United States, authors cannot put creative works in the public domain. The concept of abandoning copyright doesn't exist in US law. At best, copyright holders can license their works permissively.
Be aware that authors (except work-for-hires) and their heirs have an inalienable statutory right of termination, which allows them to terminate copyright transfers and licenses in certain circumstances.