Because a physical product is different than a non physical "product".
When you pay for a non physical product you already have paid all development of product. For example the product costs 2 million and people have paid 3 million .Why society cannot use the product freely?
You don t want trade secrets of software company .You want to use the software freely because you already have paid for the software.
It's like to buy a cola and Coca Cola forbid you to use the product to clean things.
Society cannot pay licenses forever ( 90 years is too much time)
People paid a lot for windows 95,and Microsoft will never release the software for public domain.