Well, maybe you've been blessed with a better pool of juniors than the ones I've worked with. The ones I've worked with require exactly what an AI would require -- completely defined tickets with no ambiguity, lots of deliberate review, no guarantees that what they produce is bug-free.
At least with AI if it's not working out you just shut it off and it's done. If it's a person's livelihood that process takes a huge burden on all involved.