Why couldnt they make a 64gb hdd?
Because Nintendo doesn't like making a different model of the same gen Home Console with actual difference internally. But they will need to make a greater memory size model to handle what can be downloaded from the HD eShop, so a 64 GB model would be a waste to Nintendo, plus there's the difference between the 8 GB & 32 GB models, so obviously they would make at least a 4 times greater internal memory version. Nintendo is not the kind of company to only double the internal memory. Even for 4 times greater internal memory with the deluxe, you also get a game and many other stuff, that you don't get with the 8 GB model.
That actually makes a lot of sense... Anyways, I'll be getting me a Wii U when it gets more memory on board and they sort out some of the internal problems of the actual console.
They will have all the internal stuff perfected this Summer I believe they said. So that just leaves higher internal memory.