Any sensible student would join URNU or the OTC instead. Who on earth would wish to bugger about at a non-flying UAS?
Because an URNU or OTC would be bugger all relevance to someone wanting to be in ATC, Logs, be an ABM or any other of the entire gamut of ground-based roles and deprive them of the opportunity to be around career RAF pers in an RAF environment?
Just guessing. I don't now, I was only on a UAS, didn't fly (out of choice) and then joined up. And did all that this century.