It was actually teen behavior on YouTube that made the site available for Google to buy.
The three guys who started YouTube intended a friendly site for ordinary people to share the videos they had shot themselves - with their own images and their own sound.
Their dream was destroyed by the bizarre teen obsession with uploading copyright content, causing these three decent guys to receive endless (legitimate) hassle from copyright owners. Whatever rules a website has, even if incorporating actual genuine law (copyright), teens like to challenge it.
Even this site which is a basic question and answer site, teens persist in seeking opinions (from total strangers) which actually amounts to chat which is a violation of the Community Guidelines.
Anyway, the three owners of YouTube got so fed up with the backlash resulting from the behavior of teen users, they decided to walk away from their creation (YouTube) and offer it for sale.
New owners Google, realizing that teens just won't stop their behavior - despite the numerous copyright advisories all over the site - have now commercialized the site to sweeten up record labels and avoid some of the hassle that the original site owners faced. However, the fact remains that YouTube is legally obliged to comply with the copyright owner's wishes in respect of a particular video.