It is all about proper maintenance or lack there of
When you get a customer who never removes a blade to sharpen it so spends 200 hours smashing his way through tough tufted grasses with very blunt blades and only brings in the mower when the missed strip between the blades is more than a foot or their is so little of the flute left that the deck clogs every 10 minutes then those blades will be really tight .
It has nothing to do with oiling the threads or proper tightness when replaced it is all about the spindle trying to turn the blade but the blade not turning at the same speed tightening the bolt / nut.
FWIW I have a 1" rattle gun that is good for 2500 ft lbs that I run off a Boomwade jackhammer compressor and there are some that even this will not shift till eventually it rips the head off the bolt
After that I can slip the blade off & undo the remainder of the bolt with my fingers.
The threads are not too tight, it is the head compressing the cup washers and clamping down too tight on the blade
Usually I keep a stock of blade bolts & cut off the heads that my 1/2 rattle won't shift because that is quicker than driving up to the machinery shed, firing up the 6 cylinder diesel engine, filling the 75 gallon tanks and hooking up the 1" gun ( ex coal mine ) in the hope that the head does not twist off because I don't have replacement bolt .