Missing annotations for CourseYoutubeBlockedFlag

The way, CourseYoutubeBlockedFlag , is implemented in edx platform is bit different than waffle flags annotations. Can anyone tell me the reason for defining the configurations models for them please see this file that is different from this waffle annotation logic for course level.

I am not sure why it was required earlier to define these models e.g. CourseYoutubeBlockedFlag instead of waffle annotation ?
Anyone point me where we can find the documentation about it ?