What drives whoever's the second person to implement such a flag to make it different? An explicit desire to inconvenience other "tribes" of computer users and use the flag as a symbol of an in-group?

Following a convention already established in the local ecosystem, presumably.

Though in this case I think previous posters are mistaken. My GNU implementation of head supports -c and not -b.

Perhaps it's the fact that the longopt is --bytes that caused the confusion.

How do you change, improve, or extend a standard if no changes may be permitted?

What's keeping other implementations from adding these features?

Changes with a good reason are fine, but I don't see a good reason to make the same flag a different letter.

Apparently a typo on the post I was replying to...there is no "-b" switch, it's "-c" or "--bytes" for gnu head. Though there are versions of head without one or both of "-c", "--bytes".

As noted below my post above is wrong. It should be -c.

I simply miss-rememered.