For the same reason Sram XX1 works – thicker / thinner sections of the ring mesh with the chains thick / thin inner profile so you get natural chain retention from the ring – taller teeth help too.
None of these guys seem to have the ‘hooked’ teeth the XX1 also gets though, i assume due to patent (thick / thin rings were covered by patent years ago according to the bikerumour article about the raceface ring)
Im pretty excited to try it and get rid of the draggy heavy lower portion of the chainguide i run, especially in this crap weather.
Bikerumours site has plenty of info on the raceface article….