Dark Hole at the End of the Tunnel

I spoke with a good friend the other day who is finishing up his PhD who was telling me how frustrated he is in academia and how he wants out. After he mentioned it I thought of all the people I know who finished their PhDs (or got a good way through) and have not gone on to academics (though it was their initial intention). I count eight ten right now (an eleventh hated his discipline very much upon finishing, but has since found his place), although that includes one where industry provides him as many opportunities for research as does the academy, with better funding prospects.

I don't know that many people. Why is the academy so bad at hanging on to good people?