Given the design of threadripper, it's not really "all this work" to make a 64 core model, given the 32 core model. Just pile more of the things you can scale on the chip without worrying too much about the parts that don't scale. And the same happened with previous generation. 16 core 2950X turned into 2990WX, but with a weird crippled memory interface. At least 3990X is more balanced than that.