x86 is just very expensive, especially in the DIY category. Assuming these run around the same price as current chips, the 5700G is $259 today, limited options of AM4 ITX boards, somewhere in the realm of $300. You'd have to "upsize" to mATX to get something cheaper at ~$150. Either scenario, it's well over the cost of similar pre-built MiniPC's - and that include a PSU, case, memory, NVMe, and even a Windows license.
Not too sure what AMD is thinking here, unless it's strictly for OEM's that still have a surplus of AM4 boards but somehow lack CPUs.