Of course, the creator has an interest to show this data to the advertisers if they have a good audience retention during these sponsored segments. The creators that want to hide this probably can be assumed to have a worse retention… So the advertisers can just ask for the data and know how much money that ad space is worth, and make decent estimates even when the creator refuses to share that data.

In the end, that data may very well influence how much the creator receives.

The creators sell adventisement space and want the advertisers to know that their channel is a good investment, so the more they can prove to the advertisers that their sponsor segments arent skipped, the more they can charge for it.