Magic circle trainees, apparently 1/3rd went to Oxbridge and another 47% went to RG Unis

The former stat seems a bit punchy to me, given approximately making up less than 1% a year of each graduating class. ( Legal cheek)

Don't they take on about 100 each, every season.Yet I read somewhere the Big 4 have only about 5% or so of their graduate intake who are Oxbridge, and they taken on thousands each year in the UK alone. Why do you reckon there is so much disparity?