You're overlooking the possibility that some may have eaten less at McDonalds or bought fewer candies in order to save up more money to buy those PC games if piracy weren't such an easy option.

It's not as if kids rigorously budget their money and have a "video game" line item which cannot be exceeded. If they could easily sneak into movie theatres or hockey games and never get caught, they'd do that too and spend the leftover money on something else.