User blog comment:EthanKoenigsberg/These weird videos - 8th February 2015/@comment-25923362-20150223004118/@comment-25802715-20150223010941

Because they can.

What if they want to test how often their videos gets viewed, otherwise they should had private the videos.

Maybe they need to test how it looks like on youtube. This goes with quality, the screen .etc.

How would it look on mobile?

There's lots of things you can do