Remember that over 3/4 of Oxvrudge applicants (varies according to course) don’t get an Oxbridge offer anyway. So Durham can’t afford to be rejecting those b good candidates who may well have Durham as their preference…or not.
Top tier unis know they are always one of 5 on a candidates UCAS form. They don’t know where else someone has put, where else will offer and who will firm, insure and decline them. They ALL have to over offer because of thus - Oxbridge less so, but places like Durham, Edinburgh, St Andrews, UCL all know significant numbers of offer holders won’t firm them but one of the others, so HAVE to over offer. They use complicated calculations based on take up liklihoids based on previous data and as offer holders start to decline, firm and insure get a bit clearer pic and can make further offers.
Yes, they might well make some offers to those who meet the minimum course requirement rather than give all the offers to the very top applicants and might not use a fully tiered system like some places do: tjere may be different probabilities of firming from different types of candidate, but they use the PS a lot and focus in Lnat essay.
Every year some get an Oxbridgr offer but not Durham…..or not Edinburgh or not Imperial or wherever. Some of these non Oxvrudge courses will gave more applicants per place…and with such a lot of good candidates, great candidates don’t get offers (including to Oxbridge)
There is NO decision to reject possible or likely Oxbridge candidates. Given 3/4 won’t get the Oxbridge offer, they are exactly who Durham want…and other top unis want too.