The 16 bits of the address placed on the address bus can't access the whole memory.
Thus a more complex memory interface control is needed to latch the first part of the address and then the second part (because the microprocessor will end in two step.)
For 32-bit address, one may assume the first half will decode to access a "row" in memory, while the second half is sent later to address a "column" in memory.
In addition to the two-step address operation, the microprocessor will need 2 cycles to fetch the 32 bit instruction/operand.