Well, yes, there's no profit in deleting files, and it requires some sort of post-judgement oversight to ensure compliance. When music revenues are down in general (even once you've factored 'lost sales'), the industry would much rather 'let you keep the music' so long as they get their cut of the pie. Once they've been paid off, they don't argue any more, until it is time to collect again. It's a variation on the old RICO protection racket. :D Besides, deleting the files might lose them promotional exposure and fans.