And the many, many hours of video (or film) that are shot, plus all of the audio, and all that, maybe hundreds of hours, has to be edited down to a half hour to an hour or so.
That's not always easy, and its rampant all over youtube as I have seen any number of videos where a 15 minute video could have been done in 5 minutes.
I have seen some videos where the person just rambles on about...mostly nothing....for 45 minutes.
I dont do much of that stuff anymore, but I used to keep hacking away with the delete button until my video was under 7 minutes...if at all possible.
I figure a significant number of youtube viewers (the ones I'm aiming at) are not interested enough to even click on videos that are over 10 minutes or so....but most of us will click on 5 or 6 minute videos many times a day.
And for documentaries, you have all that post production stuff......fact checking, re-dubbing, foley, acquired media and the rights to use it...legal issues, licensing, etc etc etc...
And when its all said and done, it takes a LONG time to count the piles and piles of money you made...