When it comes to motherboards, they have to develop the slot / physical form factor for the memory chips and get motherboard manufacturers to begin adopting it, whereas GPU manufacturers can just begin integrating the new memory on their boards when they feel the price/performance ratio is worth it.
(edit) - For clarification, GPU’s don’t have sticks of RAM the way a motherboard does. The memory is just soldered on the GPU along with the rest of the chips.
When it comes to motherboards, they have to develop the slot / physical form factor for the memory chips and get motherboard manufacturers to begin adopting it, whereas GPU manufacturers can just begin integrating the new memory on their boards when they feel the price/performance ratio is worth it.
(edit) - For clarification, GPU’s don’t have sticks of RAM the way a motherboard does. The memory is just soldered on the GPU along with the rest of the chips.