Training has always been seen as a cost rather than an investment by ANSPs.
The beancounters see it that way, there is no productivity to be measured from training. The beancounters like to see we have X controllers generating Y income, so Y/X is the productivity of each controller. The higher the number the better management look.
In training they like to see X no.of trainees and Y money spent on training. So Y/X is the cost to get each trainee out of the College (not rated). The lower they can make that number the more efficient the College management look.
They, initially, don't worry that the trainees coming out may not be as well prepared as they should be, that is someone elses productivity issue to worry about.
A good ATC instructor usually should have had extensive experience in doing the job, and an ability to teach and train. Sometimes these are pretty rare.
Also if you have been doing the job for years, chances are that you have had to do a lot of On The Job Instructing, and might have ' trainee fatigue '.
ANSPs are probably looking for newly retired controllers who aren't willing to let go just yet, or aren't ready to start playing fulltime bowls, golf,hang-out with the missus, etc. They are hoping to get people who already have a retirement income, and are keen for a part-time job. Hence they try to offer lesser wages.