Paranormal Activity was bullshit. I remember how people were hyping it up as the scariest movie yet, and how people fled the theater in terror over how scary it was. It took a Spielburg-approved jumpscare tacked on at the end for it to not just be people reacting to noises in their house. At least with The Blair Witch Project, it was released in 1999, so the marketing campaign was focused on the possibility that the three actors might've been missing with very few resources to find out if it's bullshit or not. For PA's marketing, it was heavily reliant on audience cameras showing how scared the audience was from watching the movie, and word of mouth that it is a phenomena because magazine articles said so.