Oil viscosity - why the 20W-50 BS?

My old factory manual for the 77 Gran Fury which was used for police use said for HD use run straight 30 or heavier oil--even in cold temps

The only thing between the crank and the bearings is a film of oil--why racing oil is still sold in straight 50 weights

Yes it does drag more, does put more strain on the oil pump shaft and might well not be needed in many cases but when the oil wedge is gone, bearing spin, cams go flat and things get ugly fast

The hotter the engine temps, the thinner the oil becomes.