If you follow the link, you'll see that there are no examples of data in the format and the README declares things like that it will provide a BNF when the specification ready. The context seems to imply that it is in an early implementation stage and not ready for non-enthusiast consumption. Also, last updated in 2014.
EDN has a few limitations regarding encoding custom types (tagged literals), and also performance in general. I understand both Transit and Fressian are possible evolutions addressing these points.
What's missing is major projects using it I think. Note how for every example he lists the big players keeping it alive.
From recollection it’s the native data transmission format for Datomic (which is driven by Cognitect/Nubank). I think there is a little bit more to the bias’ of EDN (mostly driven by language preferences in this case).