Can't access icloud videos offline

With most of the videos in my Photo Library on my iPhone 7 running iOS 11 I need to be connected to the internet and it starts downloading them. Even if I have them saved as favourites.

Shouldn't iCloud library be creating optimized versions of the photos video on my iPhone I don't want to be downloading videos every time I want to research a video I have taken.

The Photos.app says all my videos and photos have been updated.