Sharing answers to top q's we’re seeing about the thumbnail experiment: – Custom thumbs aren't going away – 99.7% still see the creator's custom thumbnail – A lot of creators use auto-generated thumbnails, this test helps improve them for those using them: https://goo.gl/A7oDmr
So I'd say work needs to be done on either a) being more visible in how you announce it, or b) getting people used to where to look for announcements... or a combination of both.