my opinion a few reasons.
let's talk about the number of hours needed to become an ADI, many PDI's believe that 40 hours training for part 3 is all they need to cover all the PST's and then it’s time to take the test. What is not explained is that this only covers the hours needed to obtain a trainee licence, and in many cases does not give adequate training to successfully pass the Part 3 exam. A trainee should carry on training until they are capable of passing all 10 PST's with confidence. You cannot put a number on the hours needed.
So whoses fault is this? It's split between the training organisations and DSA. The large training schools often run franchises and are keen to ensure that the franchises are let out as much as possible. After all it is a business that has to make a profit. At a meeting recently these training organisations were described as "Sausage Factories"
DSA have a part to play in this by letting PDI's have a Pink Licence even though they have never seen the person applying for it, or know the standard they teach at. Surely the DSA who receives £125 for this licence could have an assessment test to see if the person who is applying for a PDI licence has reached a certain minimum standard. This would ensure that The PDI knows if they are at a good standard to teach, the public have a certain level of protection against badly trained PDI's, and even DSA get to improve the standard of PDI’s, which should lead to a better pass rate on Part 3, plus they have an extra income. Everyone's a winner.
After the licence has been granted the DSA don't do any follow up on how the PDI is progressing, they are supposed to ask for a report showing that a further training of 20 hours during the licence period has been done, but it's my experience that this is never happens. Also after an unsuccessful attempt at part 3 further training should be documented and be given to DSA. Again in most cases this doesn't happen.
Trainee licences are not a bad thing, they are just run badly. Many instructors on the register wouldn't be there if it wasn't for the trainee licence. So why are some of the National Associations so set against them? They say it's to protect the public, but it's my opinion that if you want to protect the public then tighten up on the training organisations, and DSA have to look at themselves and ask many questions why they are allowing this to happen.