Who knows the reason(s) ... internal politics, tradition ("that's the way we've always done it"), vested interests, "closed shops", ignorance (especially the ignoring of government regulations and/or official guidelines), pressures from manufacturers and suppliers ... etc. etc.
In my own "adventures" I've always tried to steer clear of all that stuff, and retreat back into the Real World of volts, ohms, pressure (psi) et al ... not to mention pounds/dollars/riyals and hours/days/weeks. Logic and simplification (that is:- "think simple") has generally seen me through OK.
I'm also reminded that in the lab(s), a few too many ohms on a mains cable is nothing compared with the other risks (that is health risks to staff, including the biomed) that usually lurk in there.
