Look at the size of it compared to the Intel CPU. That thing is huge. What are the usual node size SSD controller manufactured in? 28/40nm
(Usually bigger silicon has more pins, and vice versa, but not necessarily)
But this is not the case if they stack the flash chips with the controller chips. Then only a few external pins are needed for communication and power. But the flash chips actually need the silicon area for all those tiny flash cells.