[tokenadult]

Language as identity does not explain the failure of Esperanto.

True. Lack of a large and interesting network (as you say) and some remarkable design blunders

http://www.xibalba.demon.co.uk/jbr/ranto/

are what explain the failure of Esperanto. The MAJORITY of people using English worldwide at this moment have no national identity in common with the English. (I have English ancestry, but it is the smallest part of my ancestry, and the majority of the population of the United States is of non-English descent, and yet uses English as the primary language of communication.) People learn English not because English has any particular virtues as a language, and certainly not because they have an identification with Anglo-Saxon heritage, but simply because English is an available tool of communication with unmatched network size. You and I can have great conversations with interesting people from all over the world in English, as we do every day on Hacker News.