It's a fascinating experience. How being a good writer and software engineer go hand in hand. If my library is not easy to understand, my book won't be succesful. I'm constantly going back to edit the library to make sure the book / related concepts can be grokked.
I feel this is a fairly general truism. Great software engineers are often technical writers. Both involve understanding what the 'reader' expects to see, needs to understand, and how the whole narrative/program fits together cohesively. I'd encourage anyone who wants to up their software engineering game to work on their writing skills first.
What I meant is that in real world, due to times constraints, they are. As a sibling poster commented, working as a hobby ends up being a work in itself, so doing both things ends up being, effectively, overtime.
And as a consequence, all the general considerations about overtime apply.
For some people, their hobby is technical writing.
Saying that they are mutually exclusive would be like saying that being an engineer and doing puzzles is mutually exclusive because they both require a lot of mental effort.
Or being an engineer and a musician are mutually exclusive. It's a silly thing to assume that technical writing is somehow different from any other hobby.
Which is why it is not happening. The actual rest time and hobby is when you do it whenever you feel like and stop how you feel like. Once you make it project and treat it seriously, it is work.
Also, other stuff that is done after work: cooking, cleaning, shopping, picking up kids and talking with them, sport to be healthy. These amount to not exactly small chunk of time.
That there is a certain number of engineers who have a mix of talent and resources (=time), so that they can exercise software engineering and high quality technical writing?
They are an exception. Almost all the engineers I know (with one exception), who also have a regular life (roughly 40 hours engineering/week), have little time to dedicate to technical writing. As a consequence, it's not unreasonable to state that, in general and in practice, software engineering and (regular) technical writing are mutually exclusive.