Imagine if Adobe, say, had come up with a way to do perfect DRM so that it was impossible to pirate Photoshop back in the days when it cost several hundred dollars.
It's probably true that a huge number of the people who pirated it back then would not have bit the bullet and coughed up the hundreds of dollars for a license, and so them pirating it did not represent a lost sale to Adobe.
But...I doubt most of them would have thrown up their hands and said "I can't pirate Photoshop...so I'm just going to give up on graphics editing!" or decided to just do their graphics editing all in MS Paint.
A lot of them almost certainly would have bought some other commercial graphics editor that is much less expensive than Photoshop, such as Pixelmator Pro for around $40.
That's where the lost sales from piracy turn up--in the sales of the less expensive alternatives that people would have turned to had they not been able to pirate what they pirated.