The problem is that nowadays nobody wants to retrain you for another rating, because it costs money. If you hold a valid ATC licence, you are usually quite well paid and this salary remains during your training. It generates a significant cost. And today's ANSP must be 'cost-effective'. It's cheaper to hire a freshman, pay him some minimal salary and train him then even if the risk for him to fail is higher.
It's saaaad, because not everybody wishes to do the same thing for his whole life. Switching to another rating helps to avoid boredom, because even if ATC is fun, no fun remains fun for 40 years.
Yes, I know that Heathrow Director was absolutely content doing the same thing for forty years.
