Blair Witch Project was a huge success. The entire movie was a build up to the final (and confusing) scene.
The film industry had no idea what to make of its success. It didn't fit the five act screenplays they were taught in film school and few directors would ever allow more than a few lines of improvisation much less an entire movie. They tried similar viral marketing campaigns and they failed. Eventually they forgot about it and it was business as usual again.
The industry reacted much differently when Easy Rider became a surprise box office hit. At least that movie was conventional construction and some studios were able to learn lessons from it. The main one unfortunately was that you could make movies for a lot less money.