My reasoning is that they are normally transmitted as strings in JSON, and you could use an identifier like DateTime("2025-11-02T02:33:00Z") if you need to be explicit.
Making them part of the language would increase the complexity of parsers - how would you validate that a date is actually valid? It's doable (YAML and TOML do it, after all) but requires extra steps.
note that a DateTime w/ a UTC offset is significantly different from a DateTime w/ a TimeZone (+ optional Calendar), aka ZonedDateTime. ZonedDateTime(July 26, 2035 10:15:32pm in Instanbul) may not necessarily always be at today's value of Instant(July 26, 2035 10:15:32pm in Instanbul). If you are going to support date/time, you should not use the word "DateTime", "Date", "Time" in a way that is ambiguous (is it a ZonedDateTime, or an Instant?), or forget to include support for ZonedDateTime.
MDN page on JavaScript's Temporal library gives a good overview of the difference between the two; today's practice of encoding Instants as ISO 8601 strings in UTC (Z suffix) or at a UTC offset is okay for ephemeral data-in-motion that will be used right now, but is not a good practice for persisted data since time zones, DST rules, etc change all the time. Temporal is the JS-specific API, but these concepts apply to all handling of date/time/etc data in computer systems.
That said, v8 plans to use [temporal_rs][] as their Temporal backend.
Temporal: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...
temporal_rs: https://crates.io/crates/temporal_rs
You can encode extended ZonedDateTime information to string following this RFC [Date and Time on the Internet: Timestamps with Additional Information](https://www.rfc-editor.org/rfc/rfc9557.txt)
Although given the feedback I've received, date/time might get included into the format.