I think a lot of attention to test results is paid in selection of candidates for interview, it would seem for STEM subjects at least.
Looking at the stats, some very high-scoring candidates don't get accepted at interview, which seems to be crucial - it could of course be an off day for the particular candidate.
I was later told that I was accepted for English, many years ago, because of a strong interest I had in a particular genre, which came across in one of my exam essays, and which we then discussed in interview (I thought the interview had gone badly).
Andrew Lloyd Webber got accepted for history in significant part because of his niche fascination with the architecture and history of castles, according to his autobiography.
Enthusiasm, engagement with the interviewers, luck on the day. And there is inevitably a strong element of chance, with so many very good candidates applying for a limited number of places.