I noticed that with music videos. They remove the release date, remove it from the video section of the channel and shove it in something called releases on there.
Weird change.
Music videos are a special case, because I think the majority of them were uploaded to Youtube in 2009 when they launched the Vevo service. Everything from Video Killed The Radio Star to I Got A Feeling were uploaded to Youtube "14 years ago."
A lot of changes look wierd on the surface from the companies, these are experiments for figuring out how to extract more money.
In this case my guess is people constantly look to seek out new content and avoid older content. If people don't know, that could lead more general engagement then baseline and therefore an increase in revenue.