Back in the '70s I was buying used tires to stay away from caps. Had a real good week on a illegal poker table. Converted Dayton wheels, 10.00 20 to brand new 11.00 22.5 on Budd on the drivers. Less than 120 miles one of my new tires came apart removed a fuel tank, beat up the sleeper and left door of truck.
I never was one to buy recapped tires but when I bought new unless they where a size only for front I plan to cap them twice, unless one goes flat. And over the years, on the trucks I drive myself, I have thrown virgin tread as often as caps.
As for why caps? Driver looks at a ruined tire with 1/4 inch of tread left, "It was about wore out anyway" Owner looks at same tire, "well it was about to make me money"