Oxbridge’s teaching methods reward good talk
In my experience, Cambridge University Engineering Department rewards those who can at age 19 show on paper a sound grasp of all branches of engineering, from vector calculus, to materials science, to the physics of a transistor, to thermo dynamics.
Those who can do both that, and also speak well, are often 'poached' into consulting and banking, whereas those who can only do the former tend to pursue more technical fields. But to blame that on Oxbridge seems unfair.
On an unrelated note: I've worked with many Oxbridge graduates of Humanities, Classics (Greek, Latin) and English Literature - all of whom (by selection of my firm's hiring process) are very numerate. I.e. the two are not mutually exclusive.