Youtube Webapp UI design

I'm learning user design and user experience subject and part of learning I look-up to the top websites for analysis and understanding the subject matter.

I was recently watching a random video on Youtube on a web browser. I notice the content of the video is not interesting then I start looking for much better suggested videos on the right side of the video player, then I notice as I scroll down the currently paying video also scrolling.

I was wondering why didn't Youtube consider keeping the video continue to visible yet I can scroll through the suggested videos?

Personally I like to see video continue to be visible even when scrolling through video suggestions or comment section.

Thanks in advance!