Not at all. But there are culturally rich languages with even fewer speakers then Esperanto, and people still learn them. Consider for example people learning ancient Norse, so they can read the Icelandic sagas in the original, or Ancient Greek, or even Klingon or Tolkian elvish so they can understand a fictional Klingon opera or Elven poem.

When you learn Esperanto you get access to a specific literature not available in Indonesian or German. That might be worth it for some people.