Well, it's an interesting point. Me, when it comes to drawing for my comic, I do happen to enjoy the end result more than the creating part, but for me, my satisfaction in writing is more immediate and tangible. I play with language, unique voices, interactions... I see characters and worlds develop and evolve with sentences and spaces, all from my own hand, and easily reversed with a backspace.
I would say it doesn't have to be so different towards enjoyment found from playing selections of a music piece or hitting a tennis ball back and forth. What is the "end product" when it comes to these things? A trophy? Applause? Success, perhaps. Approval. In which case achievement may sound quite universal. But all the "training" that comes before then, it doesn't mean the process has any less merit or authenticity next to the end goal.
Perhaps take something like fishing for example, a hobby quite clearly intended to be oriented towards the end product. If the fisherman returns home having caught nothing the entire day, maybe he is less enthusiastic than as he may be on a more fruitful trip, but there is no reason to say that he didn't simply enjoy his cherished hobby. But the commercial fisherman whose job or prestige depends on the end product, at the end of the day he may prefer not to refer to his title as "hobbyist".
Hobbies are very personal things and can be trained accordingly, indeed valued accordingly. Great writers may be able to accommodate efficiently to their audiences, but perhaps some hobbyists value the hobby more than the market. Certainly, lack of dedication doesn't mean lack of passion. However, dedication at the expense of passion, I consider unnecessary.
I heard a quote once, from a designer for Lego, something along the lines of "When I could find enjoyment in the most mundane of task like building a toilet or a telephone poll, that's when I knew I had a job". Probably not quite so dramatic, and of course not every writer seeks a job in the field, but the meaning is clear.
If one actually wants to orient a hobby into a habit, I say train the hobby accordingly, and "habit" may develop naturally. Maybe it isn't the most efficient or indeed effective. But I think it's how one keeps their hobby as a "hobby", no matter their earning, audience, or end goal.