If the job paid £30,000 a year top end, would you still be suggesting it should be a graduate position?
I've met a few people during my time as a HGV driver who seem to think that by virtue of having a degree they are entitled to earn more money than those who didn't follow the higher education pathway, and look down on jobs that enable "uneducated" people to earn more. Particularly where I currently work where graduates with responsible jobs earn way above the average, yet still less than I. What they fail to see is that they earn say £40k, but they work 9-5 Monday to Friday. I sacrifice months away from my family every year, not being able to participate in hobbies, and generally having a much lower quality of work/life balance.
The ability to drive well, be it trains, HGVs or even cars is in my opinion an innate skill that can only be taught to a certain level. There are plenty of educated people, who have been passed competent to drive a car, that struggle to negotiate roundabouts in the correct lane, have no sense of direction or geography, or require a rest stop for a 3 hour run down a motorway because the specific type of focus require is mentally draining.
There's a reason why certain industries seem to be a pipeline into the railway industry (police, fire, military, sometimes HGV/Bus drivers) as seen on here, as those industries nuture the type of temperament and mindset that creates a good, calm under pressure, safety conscious employee further down the line.
If you make driving, and let's say signalling, graduate positions, or even created specific degrees in those disciplines, you would be cutting off a massive pool of applicants with the most important asset that I believe Network Rail/the various TOCS look for. Life and work experience. Many on here, like myself, are looking at the railway as a second, or even third or fourth career.
It could well be my own projection here, but this topic smells quite a bit of "Keep the well paying jobs for the graduates that have "earned" them, leave the school leavers to the minimum wage"