Fundamental reason why RAM is faster then second storage device
Due to the different topology and the fact that you're using tunnelling, NAND must be erased in blocks before being written to. This means doing writes becomes a two step process. The topology increases bit density but makes it more difficult to perform random accesses.

DRAM doesn't have this limitation, since it's just a capacitor, with basically a wire to it, you just charge and discharge the capacitor. There's no concept of erase before write. DRAM's topology also allows virtually random accesses so there's no penalty there when performing writes because you don't have to erase entire blocks.

Having to use quantum tunnelling for NAND doesn't help either.

NAND Flash 

DRAM