That's what I'm thinking too, Kevin. I feel like these old metal vacuums aren't really used for house cleaning anymore. They've long since been relegated to the garage or barn (and here in Florida, that unfortunately means humidity, and rust).
Most of my finds of these vacs seemed to have been living their later years in some dusty environment, and separated from their tools. Probably used for car cleaning or picking up sawdust.
When I go to estate sales, typically, there are newer bagless plastic vacuums, or if anything high end they had a newer Kirby or Rainbow. Very rarely have I ever been to a house and saw a Hoover Convertible, Eureka F&G, GE or something from the 1970s or older that appeared to be the "main" vac. If I found something like that, it had been long banished among other dusty junk.