[ArchReaper]

>Why can't we just watch YouTube videos in Chrome on a mobile device?

Because Google owns Youtube.

Google's primary business is online advertising.

Full-blown mobile browsers could have ad-blocking extensions, which Google does not want to happen on Youtube.

They purposefully attempt to stop people from being able to access Youtube on their phones outside of their official app.

There are restrictions on certain videos w.r.t. if it can be played on a phone or only on desktop - I don't know if this is licensing (music, etc) or what, but they care quite a lot about this.

They also have Youtube Red, which is a paid service that lets people play videos with their screens off, which you could theoretically bypass if you aren't using their app.