Not all creators become very wealthy from creating, and not all creators create their best work (or work at all) early in their life.
You have raised a very good and valid point here. If copyright lapses on the death of the creator, say we have two people, Creator A and Creator B, who both live to be 80 years old.
Creator A generates a masterpiece work when they are 25 years old. In the 55 remaining years of their life, they collect income from the work, and leverage it to build a fortune to pass on to their heirs.
Creator B creates an equally masterful work (yes, it is impossible to quantify creative quality, but for sake of this example, bear with me) when they are 70 years old, and only have 10 years to reap the rewards, and so can only pass a smaller inheritance to their children and grandchildren.
This does not seem equitable to me. I know some dislike the idea of inheritance and building of generational wealth, but I don't see that going away. If one built a private business, one could pass that on to descendants. No one is calling for laws saying that after someone dies, any businesses they founded, money earned, or physical material they acquired must be given up to "the public domain." Why do some want to treat creators and their creations so differently? I believe there is an infinite amount of creativity in the world; it won't run out, so we don't need to keep "refilling the tank."
All that said, IMO the eventual release into the public domain is a good thing, but not necessarily for spurring the creative efforts of others. Rather, I would like to see works preserved and passed on for future generations to see/read/enjoy, as well as get some insight into the society/culture of the time of their creation. And yes, it may inspire them, either directly or indirectly, in their own creations, but that is a side benefit. I do not want to see a work disappear just because "it won't make money" and the copyright-holders do nothing with it.