Drugs may enable and perpetuate this behaviour today, at least in some countries, but I don't think there's much of a case that they caused it. At least if they did it arose in places like the UK without that assistance.
From my experience the root is far simpler - greed. They dangle the possibility of partnership with all it's attendant wealth and status in front of the bright young things and watch them scrap it out and burn out. I have a friend who made partner with one of the magic circle firms and while the rewards are amazing, I wouldn't swap his life for mine in a million years.