As others have said, it's not that simple.
a) I buy game X, my friend buys game Y. We play them to completion, then exchange them. In the future we'll keep exchanging games as we see fit and lending them to other friends.
b) I buy a used game X from a private that completed it and is no longer interested in it. I now own the game, but none of my money went to the developer.
c) I want to buy a game, but I don't buy it day one. I wait and wait until I can buy it for a few dollars.
In all three cases more people made use of the game than there are physical copies, or only a fraction of the whole price made its way to the developers. And yet you would not say any of those is "theft" or another crime. You could say that if you really love a game then you should buy it so that the authors are compensated and keep making games you can hopefully enjoy.
But then we've moved the point of discussion from "you have to pay price P because otherwise it's like stealing a physical object" to "you have to pay a price P so that artists/authors can keep producing media". That is the whole gist of the copyright / intellectual property conundrum: it's about supporting the arts, not about treating like items what is not an item.
In realistic terms: not every pirated copy means a lost sale. Some of them are used as demos, some of them are because of DRM, and some of them are of games that the downloader would not have paid for anyway. Yes, there's some people who will use it to not pay developers. Just as some people decide to not pay developers by borrowing games, or by buying them at gamestop, or by reading a book instead until it's discounted to hell.
And we should try to make so that authors find a way to be funded to keep working. But in the era of flawless duplication and distribution of information, then have to make better value propositions. Comparison to item subtraction doesn't cut it.
PS: I'm a developer, I founded a startup and I had to develop a business model so that we're paid enough for the services we grant, even in the face of easy software duplication. Just to say that I walk as I talk.