This is because the original copyright holders of the videos, such as the production companies or broadcasters, still own the copyright to the videos, even if they are available on YouTube. By downloading and selling the videos on DVD, you would be infringing on their copyright.
Copyright infringement is a serious crime, and you could be subject to civil lawsuits or even criminal prosecution if you are caught selling copyrighted videos.
In addition, selling copyrighted videos is also unfair to the original copyright holders, who have spent time and money creating and distributing the videos. By selling their videos without their permission, you are taking away their rightful profits.
If you want to watch celebrity interview videos, you should do so legally by purchasing them from authorized sources, such as the production companies or broadcasters' websites.