Veritasium's host looks at what we all know - you can buy likes on facebook - and discovers that there's no difference at all between buying "legit" likes from Facebook and "bad" likes from click farms in far away countries. He also looks at how fake likes spread over everyones pages forces people to buy more likes and promoting posts, creating ever larger group of un-enganged fans.
The US Department of State spent $630,000 to acquire 2 million page likes and then realized that only 2% of these were engaged.
So few fans used to equal high engagement, and many fans made for less engagement, but these days click farms are spoiling the fun for everyone and engagement is down overall.