I think 8bits (really 7 bits) was chosen because it holds a value closest to +/- 100. What is regular just depends on how you look at it.

Computers are not beings with 10 fingers that can be up or down.

Powers of two are more natural in a binary computer. Then add the fact that 8 is the smallest power of two that allows you to fit the Latin alphabet plus most common symbols as a character encoding.

We're all about building towers of abstractions. It does make sense to aim for designs that are natural for humans when you're closer to the top of the stack. Bytes are fairly low down the stack, so it makes more sense for them to be natural to computers.

Unless they are Addams who have 10 fingers and 11 toes as it is known abundantly well.