It's a matter of time, which is often crucial. You can wait for the NHS to send for you, and maybe be too late, or pay and jump the queue. Had I gone private after my high PSA reading I would probably have reached the point that I am at now in one month rather than nine. So people with money will queue jump, which, if enough do it will solve the cost problem for Dave. It is now a two tier system effectively.
And incidentally you probably do know someone in my situation. It is estimated that 50% of men over 60 have some degree of prostate cancer. Much of it is relatively harmless, a small number will be killed by it. Diagnosis is not straightforward and involves a lot of guesswork.