That never uses or explains the use of "My".

It's actually not even explaining anything I imagined. It's explaining, that some people want others to capitalize the pronouns used to refer to them specifically. I was thinking of a grammatical choice to always or never capitalize pronouns uniformly. But changing grammar rules on the whims of the person being written about, seems exceptionally odd. The closest I ever heard of to that, is in the spelling someone's name.

In reality it doesn't explain anything other than to say, some people want it that way. It never goes into actually explaining the logic of that desire. It merely tries to shame people for not doing it if requested.

Honestly that really helps with context, although I think the comparison of capitalizing other pronouns with a capital I is based on a misunderstanding of why I is capitalized.

I is capitalized due to a common way of writing the letter to avoid confusion with similar looking letters in manuscripts due to how the letters were shaped, similar to some spellings are a result of the printing press where the letters f and s were sometimes switched.

Still it is interesting in an e e cummings not always following the common capitalization practices kind of way.

[...]because nearly everyone who speaks English is a capitalised pronouns user. I. The subject form of the first person pronoun. While it’s not a matter of importance to most people, it is still the proper form used in legal documents and anything else that needs to be done “correctly”. And it got that way because someone, at some point in history, felt their pronoun ought to be capitalised and convinced everyone else to generally agree.

This is as far as I got. That isn't why we capitalise "I", as others have pointed out, and if the argument held true then we'd capitalise "Me" as well, which we don't in English.

You've clearly thought about this enough that anything I say isn't going to change your mind, so I'm just addressing the actual argument being made in that opening paragraph because it's categorically incorrect. I'm not going to bother reading the rest because I'm bored already. You might as well try to fight the tide on stuff like this.

I say that as someone who got tired of people shortening their name and instead changed their name to one that cannot be shortened because it's the only effective way to accomplish the objective.