Yet I don't hear a lot of complaint about the program (or maybe I've not been listening hard enough). I wonder what the different about internships.
The biggest difference is that internships are short and low-stakes, so if something goes off the rails it isn't too costly for the managee or manager. Also, at least in tech, hiring is hard enough that interns tend to get the benefit of the doubt on "performance issues" in my experience.
On the other side of the equation, when I mentored an intern at my company, I was given a great deal of support and training in how to help them have a successful internship. This may or may not be the case for a new manager.
My code was also subject to in-person code reviews by several engineers which was extremely valuable as it made me more comfortable with the whole team. This allowed me to become comfortable enough to ask other members of the team questions, freeing my mentor from being overwhelmed by me.
It was very much a "takes a village" approach and was an extremely valuable experience. Again, though, there was also a lot of emphasis on not wasting too much of any one person's time. Mostly because the team was a bit too happy to help me out for several hours instead of doing their own (much higher priority) work.