Copyright isn’t just paying for an idea, its giving a complete monopoly over a concept. We came up with the idea of copyright to give creators a much easier way to profit off their creation (not having to compete after its created) to make sure innovation is very rewarded. That said, its still a government enforced monopoly, with all the issues that come with that, and with how much its been extended, its far past the point of encouraging innovation and instead just works to cement large companies in place, resting on their laurals rather than making anything new. Even when a copyright ends, the current copyright holder wouldn’t lose the idea, they just no longer have a monopoly on it. Disney can and will keep making Micky Mouse content, and the mouse will probably keep being accociated with them for centuries to come unless someone makes something that dwarfs the impact of Disney’s work with the character, in which case its best that it was released anyway.

No-one creates something from whole cloth. All ideas are based on things that came before them. Locking those ideas up indefinitely will stifle creativity and stagnate culture.