I think it's important to be very clear on the correct timeline. Tiny activist groups like "Sleeping Giants" put pressure on advertisers, and got a hashtag trending (back when it was easy to get hashtags trending, before Twitter changed it so that they had to manually approve each hashtag before it showed up on the right-hand sidebar). A few advertisers listened, and pulled their ads from YouTube. It was obviously absolutely incredibly insanely obvious that they were bluffing. YouTube is the most-visited site in the world after Google Search. But YouTube folded instead of calling their bluff; now here we are.
This isn't something anybody really wanted. Advertisers did it to look good for a few days on Twitter, in a very low-ad-spend period anyway (didn't cost them anything). They were planning on letting YouTube make a tiny concession, and resuming their ads. YouTube didn't have to fold; they just panicked. They could have given Fortune 500 advertisers the ability to blacklist channels their ads appear on, and it would have gone away. They mismanaged that crisis completely (and it was far from the last).