It's not because it's "hard".

It's all about the nuisance created by human behavior. Calendar, DST, timezone, all the problems you never imagined can happen and can only be met in real life scenarios, and you will meet same problem again, struggle then found out the same problem have been solved long time ago by mature library, and the solution doesn't require any smart or advanced technique, just another corner case.

I disagree hard.

Firstly because I have a great imagination, but secondly because I am old and have a lot of real life scenarios to think about.

State-of-the-art here has changed a few times in my professional career: Once upon a time most time/date libraries used a single integral type and try to make it do double-duty by being both interval and absolute (whatever that means) time by taking the interval from an epoch.

Relatively recently however, that's started to change, and that change has been made possible by people using languages with better type systems reinventing the date/time approach. This has led to fewer bugs, and more predictability with regards to calendar operations in different programs.

But bugs still happen, so this approach is still unsatisfying. One thing I keep having to worry about is distance; I record RTT as part of my events, since when I am looking for contemporaneous events, the speed-of-light actually tends to be a real factor for me.

So I don't think this is solved simply because my problems aren't solved by existing libraries, and I keep getting into arguments with people who think GMT=TAI or something dumb like that.

It's not "all about" anything: Nobody knows shit about what's happening in the next room over, and if there are 12 different date/time libraries now, I guarantee there'll be a 13th that solves problems in all of them, and is still incomplete.