This seems to be the case with most of the arts: people who aren’t artists consider them to be hobbies, not jobs, even if you actually make a living at it. (Not that that’s the case for me, by the way.) Basically, some people think arts that are “fun” aren’t really “work”–a concept at which every single artist on the planet will surely laugh their ass off–and will insist on categorizing arts as hobbies no matter how we include them in our lives.
Personally, I never considered my writing to be a hobby even before I sold any of it; it was closer to an identity than a hobby, something I AM rather than something I DO. And yet, when I engage in it, I’m often considered to be playing, or having fun, or enjoying a recreational activity–not doing my most important life’s work. Sure, sometimes–often, even!–it’s fun. But it’s work. It’s not just something I do in my spare time to kill some hours, and it’s not something I do “as a side thing.” It’s the main thing.
I recall having a roommate in college who was a business major. I was a music major and my other roommate was a theatre major. When she got mad at us, she’d roll her eyes and say “You two just go color your homework.” Because, you see, she was the one with the real work to do. And the major preparing her for a real job.
Funny how if you dedicate your life to something you love and it happens to be an art (or, sometimes, a sport), your life’s work is considered by many to be just a game.