Why not a Pi
I think Andrew's answer says it all - they're small enough to sew onto clothing, bluetak onto lego, glue to stuff, etc, which makes them a lot more appealing as they then become a project about coding for something you already own. Much as I love the Pi, I suspect the vast bulk of users are of the age that grew up with BBC micros, or even Sinclair calculators. Or in my case log tables and slide rules. And the Pi is more for new projects, rather than adding functionality to something you already use.
I do think that adding Bluetooth to the device is a valid reason for not going with the Codebug, as it ticks the other box of letting kids connect it to their phones.
It's a shame about the power supply delay, but they're not the first to hit that problem. I've seen too many other product launches hit the same problem. The part everyone thinks is easy turns out not to be. Although numerous shocks with stuff I built as a kid never seemed to do me much harm. It did teach me that not insulating mains terminals is a bad idea.