So ask yourself: If a person who made something you want expects compensation, why do you deserve to have it for free?
You're begging the question, but even despite that I can say we deserve it because that is the natural state of things. It's just not the way the world works. There is no Natural Law of Copyright that smites those who spread ideas. Talking about why we deserve it is missing the point. And that point is that it's downright unreasonable to expect the kind of draconian enforcement and effort required for their desired compensation.
It made sense to ban the unauthorized commercial publication of books, back when writing and publishing and distributing works was so difficult. Average Joe wasn't using the printing press in his basement to cobble together a few copies of a story. Average Jane wasn't plinking away on a typewriter in her free time. It took a lot of effort to put together works of art, and it was easy to protect because so few people could work against it - there weren't enough copiers. Society accepted the then-light burden of enforcement in order to make the heinously difficult enterprise of making art a little easier.
But flash forward to the 21st century and things couldn't be more different. It's never been easier or cheaper to make art. Books can be written on word processors with a fraction of the effort and printed with a fraction of the cost of years past. Quality music recording can be done for pennies on the dollar of what it used to take. Digital film and ever-cheaper-and-better cameras have made filmmaking available to the average enthusiast. And masses of people have been doing these things.
Meanwhile, it's no longer the unscrupulous upper-class printing press owners who have the ability to copy - it's as easy as clicking the forward button on your email. It's as effortless as Ctrl+C, Ctrl+V. Everyone's doing it. And you want us to unceasingly police it, to throw people in jail and take away their rights and ruin their lives, just to keep up the side of a bargain we no longer need to get art? Why do you deserve that?