What are we doing right now to each other besides banging out some symbols that have a shared meaning?
Because these have no relation to how a particular piece of content should be formatted. The fundamental mistake made by many of these legacy APIs with respect to localization is the assumption that the locale should be determined based on some property of the user, which is reflected in some OS or application-wide setting that applies to all content. This only works as a rough approximation in the small minority of cases where the user is a member of a cultural sphere / bubble where exposure to multiple languages is a rare exception, like the united states. In the rest of the world, it is an everyday occurrance for multiple languages to exist side by side, including within individual web pages, documents, spreadsheets, and other content, which is why the only reasonable solution is the one where a locale is a property of a piece of content in its most atomic form, not of the user.
1. The fact that I grew up with those formats holds little weight for me. At this point, most of the literature I read and content I consume doesn't come from my own country. And why should it? when I have access to books, movies, websites from all over the world, and my country makes up for a tiny fraction of that. With the massification of international remote work this tendency will only increase.
2. Even when working with people from my own country, I can agree with them to use formats different from the ones we grew up with. In fact, everytime we type a floating point literal in any programming language, we do it without following the rules we grew up with.
3. In the 21st century, in the context of globalization, massification of the Internet and widespread access to computing, to keep doing these things differently by country/language makes no sense, specially when there are already good international standards that we can follow. It's not that hard to learn, either. We even accept English as the de facto language of programming and software development, and that's a full natural language that we have to spend years learning.
4. In my opinion, yyyy-mm-dd and dot as decimal separator are simply better for practical reasons. However, if we collectively decide that other formats are the "international standard" then I'd follow whatever rule we decide, as long as it's not too bad.
Can you imagine if instead of using SI units, each country used their own special units of measurement? We are definitely better off with SI, standarization makes everything so much easier. I can talk to someone from Japan about meters and kilograms and they will understand without any ambiguity.
I could resign myself to Americans* being allowed to pick the global date format to save a few cycles on an operation, but frankly I don't want to. It's not that important to me, and not having aspects, albeit minor aspects, of my culture steamrolled in the name of pointless efficiently is at least a little bit important to me.
Differences create friction yes, but I'm alright with that. I would prefer a little friction to grey uniformity. You're free to think differently, but you're not the speaker for everybody else.
* I should clarify that most Americans don't seem to want this either, this isn't a jab, it's just that if we did standardise everything their choices would probably be the ones which won out.
So dates in the US are not RFC 3339, they're MM/DD/YYYY drunk-endian. And units are all US Customary, not SI. If you want something else, you need a locale other than en.US, and if you want other things (like spell check) to match US conventions you end up needing to create a custom locale.