In my experience... that's a matter of what you aim to do. If you're drawing because it's fun, that's the only thing you should aim for - having fun. Skills and a wide comfort zone are good things to have, but not everybody wants to have them badly enough to pursue it and that's perfectly alright. Don't be pressured regarding you're hobbies. That's how we stop thinking of them as fun and relaxing and that's just unnecessary.
It's different only if you want to make money using art. Then, sure, you can't have too narrow of a preference. But for me that narrow interest went away automatically when I studied art - once I spent forty+ hours on a Bargue drawing, the subject didn't feel important to me anymore. Faces, hands, whatever, I wouldn't have batted an eyelid if I was tasked with drawing a turd because the subject was simply irrelevant to the process of learning how to draw and how to see.
I have preferences in what I like to draw of course. If I'm free and I am working on a hobby project, I work in certain genres more often than not. If I'm commissioned, well why not draw that space ship I would've never drawn otherwise? If I don't know how to draw something or how to render a specific material, it's good to learn.