Sivat -
the threading on an english bb is LH on the drive side. therefore lefty tighty & righty loosey
(the convention is righty tighty lefty loosey on right hand threads)
the crank on the drive side is spinning in a right handed manner,
the friction between the spindle and the loose cups will drive the cup in a right handed direction. WHich means that the drive side cup on an english threaded BB should be constantly being driven LOOSE. But this is not the case,
However, drive side cups come loose on Italian threaded and other BB's that have right hand threads on the drive side.
The force which spins lipless english drive side cups in and loosen italian drive side cups is NOT the spinning of the spindle, but the churning of the spindle.
We spin the spindle thru a CRANK, the crank puts a side load on the spindle and the side load changes in direction like the arms on a clock. In ways that are even harder to explain properly, it is this churning motion that causes the need for LH threads on drive side cups and left side pedals