The two reasons why people quit anything are 1. lack/loss of interest (people generally wont take part of things they dont enjoy) and 2. inability to afford it (no matter how much you enjoy something, if you have insufficient funds you will not be able to do it).
The bottom line is that golf has to regain some of its enjoyment factor to stop people quitting and it has to become cheaper.
I agree with this mainy... lack or loss intrest also equals not getting better, or getting worse.
There are definite patterns how people give up, time related really, a talented 15 year old gives up because he meets a girl, bloke gets married starts a family he just has no time and funds are low... sometimes they come back, sometimes they dont. I really do not think this has anything to do with the golf course or architecture. People will pay cheaper courses if the budget is tight.
Another point not touched on is that your friend gives up and you no longer have a buddy to play with.