Why nand flash memory comes in "large" package sizes? Even in TSOP, package is too wide and "big".
Well the obvious answer is people must still be buying them. What is good for you might not be good for the next guy. Some people don't want to mess with bgas in assembly. Maybe they require 100% visual inspection of the joints. Maybe the engineer does have the space and appreciates that he/she can solder it on or off themselves.
Not every project requires or even should use the highest density smallest parts available.
High capacity flash chips require a lot of die area to store the memory array, but they don't need a whole lot of pins because they aren't all that fast, hence the standard flash package with the pins the short sides. Using a standard package means the chip can be swapped out without redesigning the board. Modern flash chips may have a high enough density to come in smaller packages as well, but the larger standard packages are probably still used often enough to justify releasing chips those packages.