Whirlpool did make a washer only version based on their design for the combo for their coin laundries. It was called a "Whirlpool Wash-a-Lot". Google Whirlpool Poly Clean Center and you might find a mention of it. They also used the design of their combination for their coin-op dry cleaner. Nobody was looking for a tumbler washer at that time. Consumer testing magazines had so poisoned the waters for tumbler washers that Philco and Westinghouse barely managed to hold a tiny market share. People who used and owned them loved them, but their reputation to the population at large was one of poor cleaning ability and, especially in the case of Westinghouse, not so reliable machines. As you have read, Philco sold the commercial laundry line to Dexter. They stopped making combos in the late 60s. I do not know when they ceased making tumbler washers, but soon it was only the Westinghouse machine and that was kept in production largely because of the apartment and condo construction and the replacement market for the stacked Space Mates in apartments and condos. Once the energy conservation folks started talking front loaders, the market for them began to increase, but there was not a market for a Duet type machine in the late 50s.
What could have made a market for tumbler washers and maybe helped washer-dryer combinations take a huge share of the laundry equipment market is if Whirlpool had bought Bendix when AVCO sold it. Philco got it instead, but if WP had bought it, Sears could have had tumbler washers and the only washer-dryer design that was really successful because of the patents on the Duomatic. Philco never had much market share and certainly not like Sears. Whirlpool never had the market share that Sears did, but they made their money selling to Sears. The selling volume of Sears was the reason that Whirlpool could invest money in the redesign of the combo. It's for damn sure they were not investing money in redesigning the top loader.