The actual criterion on which invitations are based is whether or not you're invited. No number of requests to be invited, presentations of credentials, commitments of effort, or acceptances of a charter can overcome the problem of not being invited. The institutional structure of the W3C was not designed to serve the public interest, and even the most cursory analysis reveals that there is little reason to expect it to create standards that are optimized for serving the public interest. Everyone involved primarily serves special interests, and the public is neither invited nor involved in any meaningfully institutionalized fashion. The idea that the role of software is the central organizing feature of information interchange standards is contrary to the public interest.
Software is ephemeral, while information is eternal.
Everyone owns information, while only software vendors own software. The idea of polluting all information with names from namespaces whose semantics and syntactic constraints are expressed by the behavior of a particular hunk of software is an idea that is consistent with the welfare of software vendors. The public consists of information owners, not software vendors. A list for W3C XML Developers.