Well, people work because they're looking for monetary income, in order to sustain themselves... The complete uselessness of conlanging can't be dismissed, which is what makes me admire those that have succeeded in getting far with them.
Conlangs aren't useless: they train the linguistic part of your mind. It lets you more easily recognize grammatical structures, and it also opens up an opportunity for learning new vocabulary such as "genitive" and "gerund". Yes, I know that the mentioned terms I just mentioned seem quite childish, but a lot of Anglophones that I know have no idea that their English language sports these features.
And you could argue that music is useless the same way as conlangs. Music is something that a lot of people could generally live without, but nonetheless, it helps the brain think more logically by organizing the notes into patterns and interpreting them, and it just sounds nice. Same with conlangs. It may be obscure, but it is still a fine art nonetheless.
Just my two cents.