As an example, tech journalist Andy Ihnatko is also an avid writer of fiction in his spare time, most of which he has yet to publish. This doesn't resemble his professional output at all, which are articles that get published in a newspaper.
I think the point is that when you're doing something you love, you want to keep doing it outside the constraints that exist when someone else is dictating the type of creative work you can do.
Well, that's up to him. I don't really think any editor would think Andy Ihnatko was a worse tech journalist if he spent his free time playing with his kids or riding jetskis.
When you're doing something you love to the best of your ability, sometimes it's mentally exhausting and you need to do something totally different to recharge your batteries. Monomania isn't always the best way to go. I mean, it definitely works for a lot of people but it's not a reasonable expectation.
I think the point is that when you're doing something you love, you want to keep doing it outside the constraints that exist when someone else is dictating the type of creative work you can do.