Mostly seeing the appalling job some people have done adapting a former beloved character, or the inevitable NSFW adaptations.
Imagine someone writing a story where, for example, Christopher Robin kills someone, and profiting from it? Would you be happy having your childhood memories of reading Winnie the Pooh tainted like that?
Meaning you can freely reproduce the original work, but you cannot create a new piece of work using the original characters.
Meaning, in the case of Winnie the Pooh, the original books and associated works are free to be used and shared, but you could not create a new book or comic without the permission of the estate of AA milne.
I really don’t think this is a difficult concept to grasp, to be honest.
The original work becomes public domain, and can be freely reproduced.
The characters therein are, and remain, the property of the author’s estate, and cannot be used in new work without their permission.
We are already seeing this in the real world, where Disney cartoons are public domain, but the characters, having been used in consecutive works, cannot be used by anyone other than them.
This allows a published work to be used for generations to come, but doesn’t allow an author’s legacy to be tarnished by less than quality adaptations.
And Tigger Too - Danby Draws Comics (i0.wp.com)
Source: And Tigger Too - Danby Draws Comics...
Grinchmas (sh.itjust.works)