How come the hottest niches are using VSL's instead of plain letters?

Are video sales letters better at converting compared to plain sales letter? 2-3 years ago nearly all vendors used normal text with some graphics to promote their product, now they are using VSL'S.
And the videos are damn long like 5-6 minutes, doesn't the customer lose interest when the video is very long? It seems like they don't because nearly all the top selling products use very long VSL's.

I'm wondering the secret behind this.