It's a hard fact to face but the truth is that the vast majority of children that apply to Oxbridge will not get an offer.
To be in a position to apply they are by definition in the top academic cohort and extremely motivated.
In short there is something "special" about all of them (indeed many special things).
It's why every parent on this forum will have a story about how much work they've put in, how other people have noted how exceptional they are and how we, as parents know how brilliant they are.
Not all those children will be privileged in socio/economic terms or blessed with an abundance of charisma. Some will be disadvantaged in numerous ways, such as acute shyness, MH diagnosis or physical/hidden disabilities.
I've no answer for what the magic X factor is for those who get offers vs those who don't. These threads (over the years) are awash with applicants with what appear to have "super stellar" credentials (even in context of the high standards of the company they are in) and had supposedly good interviews fail to get an offer.
A poster on a previous thread said (and I paraphrase) that her child got based on GCSE and A Level grades that might come as a surprise to some posters, but when there was told that they were all selected for their potential.
Maybe that's the crux of it?
All these children are operating at a high level in academic terms, but what they are trying to unearth are those that they feel are not "just" clever and the beneficiaries of a good education, hard work and obviously self motivated.
I don't know how they identify that "potential" and I'm sure every parent on here will "see" that in their own child (and the child in themselves).
I suppose what I'm trying to say is that that whilst re-direction feels deeply personal I'm not sure it is.
It's more like a lottery, in the sense the numbers you pick are akin to the the course and college they applied for (and how many did the same), who conducted the interview, what questions were asked the various targets set for widening participation and oh yes the joys of less offers in the COVID world etc.
Any one of things not quite working out could mean the difference between an offer or not.
I'm assuming my DS will be redirected on the 25th not because he isn't Cambridge material.
Not because he isn't clever as hell (his head of maths said he was the most gifted mathematician he'd taught in 25 years).
Not because he hasn't worked hard and pushed himself re: super curricular activities
Not because he's incredibly shy and was super stressed about his interview and thinks it impacted his performance.
But because the probability of an offer despite all the above is very low and all the statements above can be attributed to many, many other applicants.
It's incredibly tough and 
to all who are struggling to process redirection.
@sammyjoanne Lancaster is DS's second (enthusiastic) choice and he's got a good offer from them so really pleased to hear your feedback.