Where did Blair Witch Project and Paranormal Activity succeed where other films of the same genre failed?

It’s the “found footage” genre but it could also include, imo, “first person pov/amateur films” like Cloverfield, Quarantine and Apollo 18. If you have other films in the same vein, please mention and compare to BWP and PA.

What sets these two highly profitable films apart from the rest? Please go beyond the it’s an ultra low budgeted movie as the factor. I’m more concerned with how they manipulated elements of horror to tap into what could wreak havoc into the audience’s brain and walk away satisfyingly scared, terrified and disturbed.

Thanks!