At secondary school all I ever wanted to be was a vet. The teachers repeatedly tried to talk me out of it because it was way easier to get onto a medical or dental degree. The going rate for medicine or dentistry was two B's and an A. For veterinary is was straight A's.
And once qualified as a vet, there are few safe state paid jobs, you're out on your own, taking on all the financial risk of buying/leasing premises, acquiring and maintaining expensive kit, employing highly qualified staff, negotiating prices with drug companies etc, and of course paying for your own insurance and accountants.
I did in fact get the three A's and make it to vet school but gave up after a couple of years. I did another degree and got a job in the IT dept of a manufacturing company. A little while later a friend who had stayed the course showed me a salary survey in the vet's professional journal, it showed I was earning more as a dogsbody IT worker than I would have been after the same number of years as a vet.
As slowmotion probably knows in answering his own musings, one of the main reasons for the grade requirements is vet schools themselves. There were for decades only 6 vet schools and this never expanded until 2007 until Nottingham opened a vet school. If you compare the expansion of new medical schools, dentistry and pharmacy it is illuminating. In fact it almost accidentally ended up worse as under Thatcher two of them nearly got closed and got rescued so they'd only have been 4 and now 5. If you compare to pharmacy it annoys the people I work with, until the 60s it was just like Vetinary with only 11 pharmacy schools and now the numbers are disputed by different people but there's around 30, with huge expansion in the 00s.
I went to college with two people who went on to be vets and another who was turned down from vet school and a few others where we all had similar A-level grades and went on to do different things. As it turned out in that group they tend not to talk about the absolute staple diet for a vet talking about how many years they studied any more because the two vets, living in very modern times 'n' all now actually studied the least amongst our group. One of the ones who didn't get into vet school now earns a lot more than the rest of us, us other non-vets earn less. How much you earn and working conditions tends to be dictated by the company employing you. One of them waited a couple of years until Nottingham opened and went there, but has been employed by large practices with all sorts of weird and horrible work practices - 60+ hour weekend call outs being a regular feature - she's managed to escape that a year or two back.