I just can't do it. I can see why people do though. No money, not sure you'll even like the game, it's not available on your platform of choice, all good reasons. I just stand firm in my belief of supporting people who make the things I like. I do it so they have a reason to make more. I don't even get used games unless there are no new copies left in any game stores nearby. Voting with your dollars is one of the many ways every individual shapes the world. I don't even sneak popcorn into movie theaters because I want to support the theater that plays the movie I'm seeing (the food is only expensive because they aren't making enough money because people sneak in food because the food is expensive).
You give, and you get back. Piracy hurts the developers. Games are crazy expensive to make, and to think that simple mobile games ask for $1 (small fries at McDonalds, or less than a soda out of a vending machine) and took some guys about a year to make, and people who actually like it would rather pirate it. It hurts. Heck, even Crysis abandoned PC exclusivity because of the rampant pirating.
To get a feel for it first hand check out Game Dev Tycoon. If you pirate the game, you'll reach a point where your business fails because of most of your fans are pirating your games and you can't stay afloat.