Well there are still many features missing in the new Edge, that 6 weeks delay between each release would be painful and boring. I think Microsoft is first planning to ship all the feature to the Edge and then use the Beta channel to fix small minor bugs to make the browser ready for the public stable release.
I have already changed to use Edge Dev as my main browser because I like using it so much. I still would like a slightly more stable beta build. I know they are "all" really beta builds just a more stable one.