The Pi 4B was released before Buster was officially released by Debian. I don’t “think” any of the retailers had a working Raspbian release to test anything with on the Pi 4B? They had the hardware but not the OS. Only Buster will boot on a Pi 4B. I also think they were caught a bit unawares when The Pi Foundation said you can sell them now. Thats the impression I get anyway.
Raspbian Buster was still in testing when released which is why you have to run
sudo apt-get update --allow-releaseinfo-change to get apt-get update upgrade to work correctly.
Anyway, I’m sure Pimoroni will get caught up at some point. Enjoy your pirate radio, I use mine daily.