Because all higher-level components must be created out of primitive html tags with a sprinkling of attributes, and it's nice to have a convenient way to create

Because all higher-level components must be created out of primitive html tags with a sprinkling of attributes, and it's nice to have a convenient way to create those. This is the same reason why modern languages include some kind of object-literal syntax rather than relying purely on constructor functions. Even C has a comprehensive syntax for initializing objects now. E4X was just that for HTML and XML.