Still, when you look at the chronological history of canister vacs in North America, there were at least 3 manufacturers offering a deluxe power nozzle canister by 1960: Electrolux, Lewyt and Whirlpool. Singer and Sunbeam were offering deluxe canisters with air-driven turbo nozzles by that time. The question was: why did Hoover and Eureka wait until 1973 to offer a power nozzle with a canister vac? My guess would be that Eureka thought they were offering a comparible cleaning solution with the Vibra-Beat carpet nozzle all through the 1960’s. And it could be that Hoover thought of itself as the inventor of the upright vacuum - why bother adding a power nozzle to a canister if the consumer was willing to buy a separate upright just for carpets?
So my theory is by 1970, after Consumer Reports showed that the Vibra Beat nozzle was providing “much ado about nothing”, Eureka realized the Vibra Beat could not offer a comparably clean carpet and they decided to replace it with an electrified power nozzle to compete with the better performers being made by Electrolux and Kenmore (Whirlpool). Once Eureka started selling very good power nozzle canisters, Hoover needed to keep up with the competition. I think the PowerMatic nozzles came out a year later in 1974.