Maybe that indicates these are the first to be refreshed? I’m really interested to see how will this unfold. Specially the T2 related upgrade on the software and hardware level.
Edit:
Apple probably knows that the only two (well 3 actually) new machines are in a bad shadow of the kernel panic and I would just think that they want to release these new machines up to Mac's full glory. That is my explanation for the wait.
However, Apple knows that except for these machines potential buyers might turn away and go Hackintosh route or make a complete switch because they can't wait for the release. That would explain why there is Mojave picture on the image of old hardware.
I think it is a signal that Apple is sending out and that means:
"Wait just a bit longer. We are having something in works for you. You just need to give us some more time, we wanna make it perfect this time. We'll bring you the Mac finally."
The above is my hope, my opinion, my wish and my dream. And that is why I am still waiting. I'm waiting for the Mac.