It’s not even that simple. If you skip ahead during an ad, the YT servers could just keep streaming you the ad content anyway. Their servers can ensure that the next 30s of packet data you receive is an ad no matter what, so the only way you can skip it is to wait it out and close your ears and eyes. Basically the same concept as ads on broadcast TV. Which means we’ll have to do a TiVo for YT… Gross.
Their game is just to try to make the ISPs liable; they don’t actually want it enforced. In fact, failure to enforce is the feature. They paint the ISP as complicit in the piracy then sue the ISP for hundreds of millions in damages hoping for a no-fault settlement. That’s a much better revenue stream than suing someone for 10k who can’t pay it.