A simple question, with a not so simple answer

In a Usenet forum, someone asked this very simple question about Esperanto:

"It's been over 100 years, why hasn't something so simple and so useful been more universally adopted?"

This was my answer:

It's like going to parties in Spain. No one wants to be the first to arrive, so people go there when there's already something going on. That's why the parties start so late (and then last so long).
Today's Esperantists are like the first people at the parties. At least, they can pick the best food.

(thanks to Martin for the translation)

Some other good answers by other people, here.