I am not sure I understand what you are contending. While it's true that the NUC5CPYH and NUC5PPYH support only a single DIMM (I agree, not a great decision), neither of these units come with a HDD/SSHD/SSD installed, so you can choose whatever size and type you want (and whatever O/S you want).
Are you perhaps referring to the NUC5PGYH, which comes with a 2GB SODIMM, 32GB eMMC and Windows 10 Bing installed? In this case, I do agree that 4GB (in 2x2GB configuration) -- or perhaps even 8GB (in 2x4GB configuration) -- and a 64GB SSD (instead of the pokey eMMC) might make more sense, but it really comes down to what price point you want the system to meet. Adding these "extras" may push the price of the unit too high.
Perhaps the best answer would be to have a unit with Celeron/Pentium processor that has two SODIMM sockets and an M.2 connector. I am unsure whether the Celeron/Pentium SOCs have the lanes to support x4 NVMe SSDs, but I would be fine with a M.2 connector that only supports a SATA SSD regardless.
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As Scott mention before, the current integration for this device is to have a low-cost product that’s ready to use, for that reason just comes with 2 GB memory and 32 GB eMMC (like a mobile phone/tablet) to load the OS (previously installed); however the you can add more memory and a SSD/HDD to increase storage capabilities, Intel have a list of Customer-Reported Peripherals for this NUC, you can add to the current installation without damage the NUC and add more memory as well. The below links contains the supported/tested Peripherals/ Memory you can use.
Tested Peripherals for Intel® NUC Kits NUC5CPYH/NUC5PPYH
System Memory for Intel® NUC Kit NUC5CPYH and NUC5PPYH