When I'm asking an interviewer questions, I'm trying to get a read on what it's like to work there. Are there any red flags that'd turn me off? Is this a place I'll enjoy working? Do my potential coworkers seem like decent people? Does the work/life balance match what I want to see?
When I'm actually working at a place, I don't need to ask those questions. I already know the answer.
These questions are important but they are not the types of questions I am asking about. Part of determining if you want to work somewhere is figuring out how mature the team is when it comes to design decisions and the development process, to accurately ascertain this, you have to ask technical questions, the act of asking these questions is itself an indicator that you yourself are thinking about these important things and as such value them and should, to a well functioning development team with a working product, indicate that you would at least contribute to keeping things working optimally and contribute positively.
I would be worried if someone nevet asked about the thing they were going to be working on, asked why certain design decisions were made, or asked how it gets developed.
Sure, I agree. That's part of me finding out if I want to work there.
The unfortunate reality is usually you're given 5-10 mins at the end in a hasty "what would you like to ask me?" so I tend to stick to the more basic type questions. Repeating across interviewers to see what patterns pop up.
That said I'm not shy about pushing back with questions during an interview session itself, and that's where things like you're talking about can get worked in. Of course if they insist on "solve this problem" type sessions, there's less of that. But it's also less likely I want to work there. So it works out for me.
When I'm actually working at a place, I don't need to ask those questions. I already know the answer.