I very much believe they are Youtube’s responsibility. I pay to see no ads, so I don’t wanna see ads. Full stop. I am not sure how true this is, but creators say that when YT Premium subscribers watch they get more revenue. With that they should be required to mark sponsor segments which get automatically skipped for Premium subscribers.
Also I started using sponsorblock only one year ago because I think within the last few years lots of creators have overstepped the mark whats tollerable for me (promoting scams, sponsors taking up 1/3 of the video, …)