Because it 's part of medical folk-lore, is all... and it works. The medical profession is notoriously opposed to innovation, change, or challenge to 'conventional wisdom'.
It s this which prevents them from basing their dogma on fact (as opposed to 'evidence'). Bit like most religions, really.
Difficult to use the carotid arteries, because blocking them off to produce the Korotkoff sounds would cause unconsciousness
. But really, -with suitable calibration, any major artery
would be suitable.
Do remember however, that readings taken by auscultation at the brachial, radial, or any other artery are NOT true.
They only "reflect" the true pressures (generated within the left ventricle) and while (measured) CHANGES truly reflect CHANGES in real pressures generated within the heart, the actual measured values are virtually meaningless, - especially (for different reasons), without simultaneous pulse-rate observations.
This is the reason that so much nonsense is written on "Answers".... from nurse, trolly-pushers, para-medics, and sadly, even doctors, who should know better.