Hi Simon,
It’s a long story. The gist is that the docker images for previous releases were only semi-official (hosted under our aegis, but not really supported by us), and the change to 4 distributions brought us to a bit of a crisis point on this topic.
We’ll (probably) get “soon” to where we distribute and officially support an image for each edition, but we’re just not ready yet and we didn’t want to put out an image for only one of four distributions.
HTH,
Ann