The professions, and everything about them, are designed for people who don't have to work to earn a living, and who work out of service to society. Professional culture is a result of this. That's why rich kids do better in the professional environment. It's not anyone favors them because of their families. It's because they aren't ruined if unemployed for a while, so they don't fear the boss, get more respect, and handle a professional environment better.
The difference, circa 2010, is that nearly everyone has to work to earn a living. So the professional norms are out of date for most people.
This should shine some light on why interview processes are the way they are. For people who are working for love and leisure, a 2-month process from application to decision, with 2 or 3 rounds of interviews that require time off work, isn't unreasonable. For people who either (1) are unemployed and have a ticking clock, or (2) are employed but will be in trouble if they lose their jobs (which is likely if they're caught interviewing, in today's environment).
As for why it's so difficult to find good candidates, the interview process is a big part of it. Good candidates are only willing to go through with it for something approaching a dream job (for a hacker, Google Research; for a quant, DE Shaw). Otherwise, they ask their friends who they know and search informally.
Also, the fact is that most corporate environments are utterly mediocre and soul-sucking, and that hurts all but the most-established companies. There are probably 1000+ companies where a smart person could work and have smart co-workers, good pay, and interesting projects... but only a few stand out for having this reputation (e.g. Google). If you're not on this list of 20 companies, you're going to have a hard time proving that you're not one of those mediocre failboxes.