I can't wait until you find out that sufficiently old intellectual property goes public, while sufficiently old houses don't go public! Have fun blaming that on me splitting hairs when it wasn't my idea.

More seriously, intellectual property is a number of different things lumped together, and they serve different purposes. Copyright exists to encourage new works, and while you can make arguments that there are some benefits from copyright being long-lasting on the creation of works like books and pictures, it's basically impossible to make a similar argument for code.