My guess is that most of the people who added it to their goals had never thought about it until they saw that it was a popular goal, but they thought "ooh, that sounds romantic" and added it. It's just one of those random runaway successes.

On the upside, unlike "live passionately" it's relatively easy (desert dwellers and the terminally dateless excluded) and well-defined, so you know for sure when you've achieved it.