Why YouTube restrict Downloading Content??

YouTube is online video streaming website with enormous users. YouTube is bought by Google in November 2016 for $1.6B.
YouTube allows individuals to share their videos, like, dislike, create channels, subscribe channels and recently they have added story feature as well.
Apart from content sharing site YouTube restrict to download or recreate any part of the content shared by individuals.
Individuals can earn from platform via Ads. But in their recent update individuals with 1k subscriber and subsistent amount of watch hours will be able to show ads via their respective channel to earn,
Apart from main web site they have multiple mobile Apps to enjoy streaming both uploaded videos and live streaming from the content creators.
Now coming to main question why YouTube restrict downloading content.👶
Before moving to Why let's discuss YouTube API 😉
YouTube have provided API for developers to integrate the YouTube functionalities in almost every Technology which will done through acquiring access Tokens from their official site.
Link here : https://developers.google.com/youtube/v3
But this will not allow downloading content only viewing of the content.

Now let's discuss why
It is obvious that only way to intact their users to them is by restricting the content from download so that users visit again and again to view and share content available.😐

Updated:
However, No worries you can still do it their are multiple Apps available that will help you doing this.
One of which I personally recommend being a Android user is Mp3Mp4 downloader.
Do Check out this App.