3-bit grayscale is skipped on the monochrome list

Question

I wonder why this Wikipedia list has 1-bit, 2-bit, 4-bit, 8-bit grayscale. But it skips the 3-bit grayscale. Does it have a specific reason?

Answer 1

Because no one ever wanted or needed 3-bit grayscale. In general, you would like for the bits to fit nicely into a byte, so 1, 2, 4, 8 bits would fit 8, 4, 2, and 1 pixels per byte. Or 16-bit grayscale into two bytes.