I've never heard of rear brakes locking up unless the rider is club footed as said. This is weird but what do I know, I've had too many years with broken bikes to know anything plus I'm not even 50 yet.
Older bikes had large rear discs, lets say a cb900/1100f had a 285mm rear disc, that size on rear can be easily locked when applied without feeling.
I thought everyone wore trainers back then though? Maybe that was only the paddock jacketed hooligans lol
Steel toecap pit boots a donkey jacket & piss pot helmet here through most of the 80's, trainers were for training still not sure what a paddock jacket is for even now unless its for looking a twat when you are out in the car