Why don’t EXIF capture timestamps include a time zone?

Historically, EXIF stored the capture time as local camera time without a time-zone offset. In older EXIF standards this appears to have been an intentional omission: the standard specified UTC for some fields such as GPS-related time, but not for the main capture timestamp.

A practical reason is that time zones are not determined simply by longitude. They’re political/local rules, with irregular borders and daylight-saving changes, so a camera cannot reliably infer the correct zone unless it has location plus a timezone database or the user sets it manually.

More recent standards did add support. EXIF 2.31 introduced time-zone offset fields in 2016, and XMP also has guidance for timezone-aware timestamps. However, camera and software support has been limited, so many files and applications still behave in the older, minimalist way.

So the short answer is: older EXIF didn’t include it by design, partly because local time is easy to record while correct timezone handling is harder; newer standards support it, but adoption is still incomplete.