You can't just consider one question and one answer in isolation. The questions and answers add up. It's a waste of the senior engineer's time to spend ten minutes each answering every question of junior engineers who are constantly asking questions, seemingly incapable of helping themselves. The senior engineer becomes a glorified babysitter, and the junior engineers then never learn to solve problems for themselves, which will waste everyone's time in the future.
Not every problem is going to take junior engineers days to solve for themselves. I was stating an upper bound of how much rope to give them, not an average.
Besides, what happens when the senior engineer leaves the company? Sometimes "institutional knowledge" walks out of the institution.
Yes, what happens when the senior engineer leaves the company, having never shared his or her knowledge?
It sounds like you are trying to address issues during mentoring that should have been addressed during the hiring process. In my experience, all the juniors I've worked with come in with the idea that they can solve every single issue themselves, and part of my job is to show them how wasteful that is, that a simple question can save the whole team days if not weeks worth of time.
If someone walked through the door who is not enthusiastic about solving technical issues themselves...your hiring process needs work.
Not every problem is going to take junior engineers days to solve for themselves. I was stating an upper bound of how much rope to give them, not an average.
Besides, what happens when the senior engineer leaves the company? Sometimes "institutional knowledge" walks out of the institution.