Youtube Premium has YouTube remove the ads that they have control over. YouTube only has control of the ads that they add to the uploaded video, on either end or mid-rolls. They do not have control of the video content itself which is where creators add their own sponsorship stuff.
We really want YouTube to have unilateral control to determine what is and isn't an ad, and to remove sponsored advertising that they are not a part of in uploaded content? Something that would also clearly be a conflict of interest as they are an advertising partner.