The DDR5 600 series already seem to be marked up drastically. Why does DDR5 seem to add another $50 on top of the DDR4 version of the same motherboard? Is the DDR5 system licensed differently or are the electronics that much harder to manufacture?
Generally, a DDR5 MB design needs to account for increased clock speeds and data rates, and for different channel architecture. Specifically, there are things such as DDR5 running at 2 channels per DIMM (instead of one with DDR4), featuring DFE (Decision Feedback Equalization), having temperature sensors, different power management, and running I3C (protocol of the SPD Hub), which the MB all needs to communicate with accordingly. This translates to i.e. need for improved DIMM connectors on the MB etc., the R&D put into it, and probably also some changes to the assembly line.
Whether that amounts to $50, I don't know. But there sure is more involved than just to swap out one part for another.
And basically similar is also the jump from PCIe 4.0 to PCIe 5.0 connectivity, where a MB needs to be more capable to handle signal integrity issues. Whether the price difference is more about cost of parts (from in-house or sourced), or about (initially) offsetting the investment into R&D and assembly line/s, I don't know. There certainly is a bit more refined hardware involved though.