The server can't completely ignore the player, as it would have to adjust the embedded timestamps to be consistent with the skip operations, or otherwise the player won't show the video. In other words, the server would have to act as if the ad is embedded wherever you skip to in the video. Not only would it mean that users lose their position in the video when they try to skip, since after the ad it would continue in a different place, but it would also mean that timestamps don't uniquely identify positions in the non-ad parts of the video anymore, which is a nonstarter in many ways.