The basic problem is that a PSA test isn't actually a terribly reliable way of knowing whether or not a man has prostate cancer. A level of around 3 or 4 is normal for a man in his 60s, but if someone gets a test and it comes back as 10 or 20, that may well be due to a urinary tract infection, or lots of other things. The only way to know for sure whether or not someone has prostate cancer is to do an MRI scan and, if that shows something suspicious, a biopsy to confirm, and a biopsy is not something anyone would do for fun, believe me!
So basically, men tend to get tested if they have suspicious symptoms such as having to go to the loo six times a night, and lots of cases are found by chance when something else is being investigated (that's how mine was found), but there's no screening programme and, as you've discovered, many GPs are reluctant to test without cause.
Cheers,
Chris