The whole Webmaker initiative is not focused on established developers, so while it might be true that SitePoint has a lot of high technical contributors/readers, this is taken in a different context, concretely teaching consumers to be makers on the web.
True, there might be some technical bugs here or there in the app (hence beta), however the mission is the same; inspiring potential makers/developers/web enthusiasts to get involved with web technologies. As you can see, the numbers support it, every year thousands of Webmaker Maker Parties all around the world are organized by unpaid volunteers, being proof enough that this has gained a lot of traction and has impact on a lot of web enthusiasts, especially those who don’t have accessibility to a lot of learning material like we do.
Indeed, it’s not much use for someone who changes their JS frameworks like their socks, but again, this is not the context of the app here.