Phillip, what option list are you using? Is it the specific Chevelle option list published by Chevrolet or is it a list from the Internet? Is it a generic appendix at the end of an information package from Chevrolet? It has to explicitly show that they were offered on Chevelles, but looking closely it shows they didn't. Surprising, yes. Chevrolet did offer power windows in 71/72 on Impala, Caprice, Monte Carlo, plus the A33 power tailgate window on wagons (standard on the full-size wagons with the clamshell gate). I am going by the SAE published specs that you can now download for free from the GM Heritage Center. I am also going by the brochures (both Canadian and U.S.) for both Chevelle and the wagons in which they talk about power assists being available. They mention power door locks and other stuff but never mention power windows. They are also absent from the 1971 & 1972 Chevelle option lists. Have you ever seen an original 1971 or 72 Chevelle build sheet that lists A31? I have never seen one, nor have I seen an original 71-72 Chevelle with power windows. Updated or owner added, sure, but not on an original.
Like I said, other GM intermediates did continue to offer them. They used the same gang switches on all intermediates (though they were of the built-in kind in the arm rests on the Grand Prix). Today parts houses offering kits will be more than happy to sell anyone a power window kit for a 71/72 Chevelle. They fit like they belong there, but they were not factory during those 2 years.
I agree that it doesn't make sense, but let me try to explain what was happening. John Delorean was the head of Chevrolet at that point, and he was given a mandate to make Chevrolet more profitable. Option proliferation really hit a zenith in 1969, yet for all the added options they weren't making a profit commensurate with the costs of offering them. Delorean instituted a de-proliferation edict. Axle ratio choices were reduced starting in 1970, HD 3-speeds were dropped (temporarily). They also dropped power windows from Camaros for 1970 but kept them going on Firebirds. Power windows didn't officially return to Camaros until 1974 but they phased them in during the 1973 run (they switched to a Firebird console in the Camaro for 1973). Chevrolet was the value division at GM, so that may have been the over-riding corporate edict from the GM brass to Chevrolet.
Another unexpected omission from the Chevelle wagon option list for 1971-72, Rally Wheels. Also they were not on the 1973 Chevelles as an option, only as a standard item with SS equipment. The Turbine I wheels were offered on non-SS Chevelles instead. 1974 was the same, except if you ordered radial tires you could now also order 15x7 Rally Wheels on any V8 Chevelle, including wagons (but supposedly not on El Caminos; their day would come in 1975).