I'd say that its because once you have the PPL there is no where else for the PPL to go regarding flight training, without resorting to serious amounts of money. I probably would have given up a long time ago if I hadn't turned to the dark side.....
The FAA system is very different, you can bolt on extras along the way for minimal time / jumping through hoops and continuously improve yourself. I had a PPL at 60 hours and I had an IR at about 120 hours, which would no doubt be unheard of in JAR land. To get an IR here I'd need to firstly get a JAA class 1 audiogram, then pass the JAA IR ground exams, then do the course and be tested. At least a £10,000 venture I'd guess.
There are several problems with the way the JAA system is set up if you want to progress. Firstly you have this massive hurdle of the JAA ATPL exams. You can do the CPL exams but there really is no point, because if in the future you want to upgrade, you have to do the whole damn lot again???? You're looking at least a year to complete these exams, plus a couple of weeks residential course, whereas in the US I can self study for the CPL / ATP exams from a good book, then just turn up and take them for $90.
Secondly once you have spent £2700 and a year doing the ATPL ground exams, which in all honesty are interesting, but irrelevant for a light aircraft driver (B737 FMS???) and you have done the CPL skills test, you MUST then do an IR within 3 years I think, else the exams expire or something funny along those lines.
The next hurdle (or probably the first one) is the JAA Class 1 medical which you would need to pass. Not a problem if you're healthy, but anouther £400 and a day to get it done. Then the renewal needs to be carried out annually for someone of my age. In the USA they have three classes of medical, Private, Commercial and ATP. This makes perfect sense, why should a CPL or even instructor be medically tested to the same standard as a pilot who is in command of a 600 seat A380? It is nonsense.
The content of the CPL/IR flight training in the UK is fair enough, however I notice that IR training costs are hiked up extrordinarily. Some places charge £400 per hour for ME IR training. This is surely a rip off, and what is a rip off is paying £200 per hour in a FNPTII sim which uses exactly the same software as many FAA approved Sims, which cost $50 per hour.....but are not JAA approved.
The whole JAA system is geared towards airline pilots. Ideally I'd like to be a part time flight instructor in the UK (who also flys for fun), with CPL/IR FI ratings. But for me to get to this point in JAR land, I need to spend £2700 and a year doing the ATPL exams, get a class 1 medical, convert the CPL and IR and do an FI rating.....and extrordinarily expensive and time consuming quest. (I passed my FAA instrument instructors ground exam, it cost me $90 and I self studied in my own spare time.....).
Cheers