I think your analysis of the situation is 180 degrees out. They're certainly not 'outdated social clubs' any more, which is part of the problem. After all, if they were social clubs with flying attached, there would be no worries about 'restricting his ability to fully commit to the UAS programme', because even the most arduous degree courses leave some time for evening social activities. At this point I should note that the original function of UAS was NOT to recruit anyone, but to leave a good impression of the RAF among the future great-and-good (a superb example of the foresight with which Trenchard established his fledgling force).
Because UASs are now so narrowly focussed on their modern-day task of 'helping the RAF recruit the sort of talent it needs', they have a massively reduced emphasis on flying (which, back in the day, was something that students could schedule around their study commitments) and a greatly increased emphasis on things like leadership development and adventurous training (which, being group activities planned in advance, do not offer the same kind of scheduling flexibility).
I am afraid that my analysis does not answer your concern as to precisely why apparently-suitable individuals are knocked back. But I can guarantee you that it is not down to some antediluvian 'social club with flying' outlook. Probably the opposite.