So the law is within the bounds of common sense when it defines the copyright period as the life of the author plus 99 years? The constitution says a copyright

So the law is within the bounds of common sense when it defines the copyright period as the life of the author plus 99 years? The constitution says a copyright is granted for a limited time to encourage artists to create. How is Walt Disney going to be encouraged to create another Mickey Mouse when he's been dead for 40 years?