Same reason people tandem sky dive their first time instead of jump solo, until they know if they are going to like it or not, they don't want to go through all the hassle. Doesn't mean they don't want to be safe. Difference is skydiving is never on the chopping block for being banned, it doesn't require persuading voters to secure its future.
Hunters safety doesn't ensure safe hunters just like drivers safety doesn't ensure safe drivers. It doesn't make them safe, only ensures that they at least know better. You still always have to be on the look out for "the other guy". Let's face it, some people are just idiots and they are going to do what they are going to do.
Would this allow some of those "idiots" to mentor other "idiots", probably, but those same idiots already passed hunters safety, so I fail to see the difference. Neither process is full proof. At least this way, they would still have to pass the course on top of being mentored.
On second thought…… maybe a compromise would be some sort of special certification to be a hunting "mentor", which would allow a person to take adults hunting for the first time prior to taking the course. That might not be a bad way to go, it would "screen" the mentor pool a little bit.