Very high drop out rates as it's hard to study for professional exams alongside full time work. And after 3 years (or 4) at Uni, graduates are fatigued and another 3/4 years of professional exams is a very hard task.
I really struggled 40 years ago to do my accountancy exams alongside full time work, as I actually wanted to get on with life, rather than continuing to spend evenings and weekends studying/revising for 16 exams over 4 years!
My son is a graduate actuary working for one of the UK's biggest insurance/pension firms. They take on lots of graduates/interns for their various professions, i.e. actuary, accountant, HR, marketing, etc., but the drop out rate is huge. That's with something like 30 paid study days on top of something like 35 holiday days, study materials/course/exams all paid for, and a starting salary of around £35k (same for graduates and 1 year interns). He's been there 3 years and seen the intakes twice a year in his small department - they come and go again as they really struggle despite all the help they're given. He's half way through his exams and really struggles with motivation to study/revise after a 9 hour working day. Most of his department are actually "failed" actuarial graduates, they started on the graduate scheme, took a few exams, failed a few, and simply couldn't carry on, so they stayed on at lower/junior levels, so not working up through the ranks to the highest actuarial level doing the real actuarial work.
Another factor is the few who get through it and qualify virtually all emigrate within a year or so as they are in such high demand all over the World. The lure of much higher salaries, lower taxes, better living standards is just too much to resist. DS never really considered moving abroad, but he's been to so many "leaving do's" of his co-workers emigrating, that it's really put it to the front of his mind and is a hot topic of conversation among his work colleagues, i.e. discussing the best countries to move to etc.
As I've said upthread, we should be making better use of the 3 years at Uni, i.e. doing the professional exams rather than generic degrees to speed up the training process for those wanting to go into professions. 3 years at Uni plus say 1/2 alongside work is a lot more attractive than 3 years at Uni then coming out, starting again, and doing 3/4/5 years alongside work.