I think it's for ads. I first discovered this watching "Interview with the Vampire". In the UK, it's available on BBC iPlayer, but that version runs faster than the pirated version. I didn't notice until we took a break from watching and notice we were out of sync. I decided to test it by playing the pirated version at the exact same time as the BBC version. It was uncanny to hear them start out synced but gradually diverge.
The BBC iPlayer version doesn't have ads, but when playing on live TV it does have ads, so I assume that's why.