I got an email from some students doing research on international languages. They asked
Which type of language do you believe succeeds better, one developed by social interaction among people, or one developed by one person for the social interactions among people? And why?
Here's the reply I sent
Just my two cents: your question is a false dichotomy. It is useful to make a distinction between languages and "language projects". There have been hundreds of language projects, but almost none of them have gone on to be actually spoken by a multigenerational community of people. Esperanto the language was not created by a single person: Zamenhof just created the language project. The language is being created the hundreds of thousands of people who have spoken it for over a hundred years, defining its use and culture. Why Esperanto developed a community and became a language is another question. My opinion is that it had to do with the particular sociology of the time and place. At that time, the idea of a "language problem" got traction and Zamenhof's project was clearly better than Volapuk, which people had tried and found too difficult to really master. It's hard to identify what are the causes and what is simply coincidence.
Why Esperanto hasn't more widely adopted is another interesting pair of questions: why isn't it more widely adopted by the general public and why hasn't it been more widely adopted by the international diplomatic community? I don't think it is more widely adopted by the public because the idea of a "language problem" has fallen out of favor. For most people there is no "language problem" for Esperanto to solve. Most people don't perceive a pressing need to communicate with people from other cultures: they have the TV to do it for them. Regarding the diplomatic corps, again, my own opinion is that the people who are in power, who could affect the decisions, derive more benefit from the current circumstances. Why should they press to adopt some other system? The people who are at the bottom have other issues that are more important.
They wanted to meet with me to interview me, but I pointed out that there are undoubtedly lots of esperantists who live closer to them and that 
meetup could help them find local groups nearby. It's always fun to have a chance to pontificate.
StevenBrewer