> French people do use the regular order but in some occasions do write it as FAMILYNAME GivenName

The EU also likes to do this, perhaps so HUNGARIAN Dude isn't called "Mr. Dude".

My confusion there is not that an ordering needs to be chosen, but why, if you make a choice, that choice wouldn’t be capable of consistency.

Which is what I think the original list is claiming.

I'd say it's because the order varies between cultures and you might have them mixed up on your system

Not only ordering but equality. So for example Müller and Mueller might be considered equal in German.

Edit: Just found an interesting example, Linkedin orders Á after Z (where the correct in most places would be to sort it together with A), after that, letters in different alphabets (correct) then the emoticons (well, people do add that to their names...)

"Müller" and "Mueller" are actually different names. But if umlauts aren't available, "Müller" should still be represented as "Mueller", "Muller" would be just wrong.

Ordering also depends on the context. Usually "ä" is sorted like "a", but in lists of names it's sorted like "ae".