"XML" is just way too complicated

XML 1.0 was a simplification A slimmed-down version of SGML, XML's creators tended to see it as an easier way to handle document information.
DTDs were a simplification XML Document Type Definitions are similarly a slimmed-down subset of SGML DTDs, aimed once again at document information.
Namespaces begin the pile-on To address questions about conflicting vocabularies and to integrate XML more tightly with the URI-based vision of the Web held by the W3C, Namespaces in XML added mechanisms for associating URIs (Uniform Resource Identifiers) with XML element and attribute names. Namespaces has produced an incredible flow of Zen conversation plus a few practical applications since.
Schemas, Web Services, etc. XML and DTDs weren't enough to support the visions of the programmers introduced to XML's visions of a unified data format. Object, database, and distributed object expectations have since been glued to XML in a series of specs that claim to be XML or use XML in ways that obscure what's actually happening when you use markup.