I'm not expert in electronics manufacturing but have seen (took part in) new product launch. AMD demoed Ryzen in December, so I'm sure all MB manufacturers had final board design and decent qty for 0-series. At least they should have. So it looks really strange to me that some hardware components are missing. Plus, now when CPU is actually SoC, there are not so many differences in (hardware) design between different sockets. You know what you'll need for SATA, PCI-E, I/O, etc. Also, AM4 boards are actually available for half a year now, since OEM are selling BR APUs and A320 boards since September.
The biggest (not say the only) issue is BIOS. And that one can be updated anytime. MB manufacturers coud actually make large stock of AM4 boards in January, and just update BIOS before release. Whether it is in March 2nd or late Q2. Hardware would be the same. In my previous company, we have found some bug on control boards (complex one, almost like cheap PC MoBos ) few days before the assembly of final product has started. And had to update firmware on all boards we had on stock. It took additional resources, but didn't affect final product launch.
So I would say its mostly AMDs fault we have no good BIOS (and microcode and OS support...) at the launch. Which is not good for consumers, but not that bad either, since we know it will be updated in next few weeks or months. But supply issue is mostly MB manufacturers fault. I mean, they (some of them) actually admitted they put priority on Intels 200 series. Of course, there is minimum time from order confirmation to shippment, but that's the industry