They would still need a new motherboard to use newer memory types, because the modules will have different connectors. They might need a new chipset if the newer memory type wasn't actually addressable with the FPGA (not enough pins, not enough signalling capacity, not enough voltage flexibility, etc).
For the majority of users, they don't change the cpu, motherboard, or memory for the life of the computer (in many cases, some or all of these parts are soldered to the board). Paying more for flexibility that will never be used isn't good for anyone.
Ryzen has seen improvements to DDR4 module support with each generation and to take advantage of the latest generation you may need to upgrade your motherboard to one with the latest chipset, depending on vendor support. Even if your older board supports the newer generation, likely you have a more limited QVL for DDR4 modules, so compatibility and perf may be limited.
This is why I implied it had limited impact, though there is some truth to boards with newer AMD chipsets offering better memory support.
This was a response to parent comment stating it was greedy behavior to try to get consumers to buy new motherboards with new chipsets, when the chipsets have little impact on RAM compatibility/support.