It's in their About page (https://readtapestry.com/about#) too:

> It's simple: tap to move forward in a story. There’s no going back, so take your time—that’s the whole point!

Not allowing the viewer to know how many slides there are and navigate between them is a terrible, terrible idea.

I think Mike Bostok's Stack is worth a mention: http://mbostock.github.io/stack/#0