trio
I study Spanish because i live in the USA and Spanish is the de facto second language (almost all of the time). But Spanish wasn't useful in Turkey, Japan, Cairo, etc. where i did use Esperanto. I wish i could learn all the languages of the world, but i'm just not that good at it. Esperanto is easy.
But, more than that... In the USA a native Spanish speaker is (too) often discriminated against. As a non-native Spanish speaker i am always on the outside of conversations in Spanish. Esperanto is meant to be everybody's second(!) language, not be a homogenizing language for the planet. Esperanto speakers are all non-natives (actually there are some natives, but they don't have special powers :) so we Esperantists meet as equals.
To riff on what somebody else wrote, if a client said i had to learn Haskell, i'd be happy to be paid to do so. My "payment" for knowing Esperanto is the community of (mostly) intelligent, (mostly) compassionate, and (mostly) generous people i've met using it.
YMMV
trio