Why are there no elements of the type DateTime?

During analysis of the data requirements sources, the XML Structure Task Force (XSTF) found no evidence of the neccesity for mandatory use of date and time together. Many sources had defined both date and time components, but there were no components of the type DateTime.

The XML Schema DateTime type uses ISO 8601 format and does not permit the option to use either date or time without the other. This means that if a component is of type DateTime, then both date and time are significant and must be present. As a result, there is no way to indicate that time is insignificant or unknown. The XSTF believes that this could lead to potentially confusing or misleading data. Therefore, it was decided to use xsd:date and xsd:time should be used optionally and independently.