From the real-world hardware perspective, there are several reasons that memory chips come in various organizations.
The wider the memory is the more pins are required on the chip. An 8-bit wide memory requires 8 pins for data I/O, whereas a 1-bit wide memory only needs a single pin. A chip's pin count dictates it's size; the actual IC is usually much smaller than the packaging.
There are times when memory width needs to be something other than a multiple of 8. For example, memory with parity checking needs one extra bit. Error correcting memory (ECC) requires several extra bits.
Here's an example: a 1M x 9 memory module. The 2 HY514400AJ chips are 1M x 4 memories and the HY531000AJ is 1M x 1.
(In this example, the chips have the same number of physical pins, but the HY531000AJ has 3 electrically unconnected pins. It's easier for the manufacturers if the chips have the same physical form factor.)