Not sure (officially) why, but ASUS released new UEFI for its ROG Strix X570-E Gaming motherboard which brings full support for the OG Ryzen chips. So far, this is the only AMD X570 chipset to support 1st gen Ryzen CPUs.
This includes Summit Ridge CPUs and the Raven Ridge APUs.
Reason for CPU support limitation
The reason why ASUS was able to extend the support backwards is because of its BIOS chip. The ROG Strix X570-E Gaming has a 32MB storage for its BIOS. While it is not the only X570 to have a 32MB single BIOS chip, its the only one to support it. Nobody probably asked but Asus rolled with it. This is likely done to cater to some extreme overclockers(?). But Asus was able to. And hence it did it.
BIOS chip limitation is usually the main limitation for extending Ryzen support depending on the chipset. This is very clear with the way X470 “can” support Ryzen 4000-series CPUs and APUs with permanent drawbacks. Motherboard manufacturers rely on AMD for its AGESA updates. But it also relies on BIOS chip size. But the AMD X570 motherboards should have unrestricted support for the upcoming Ryzen 3000 Matisse Refresh and the Ryzen 4000 series APUs and CPUs. We’ll just have to wait and watch until everything is released.