Hi, Nancy. 50 years ago, most hardwood had a varnish finish. Polyurethane is a varaition of this and really much better, if you use a good floor varnish. 70 years ago, there were still some oiled finishes around but these did not have a nice shine or offer any real protection to the wood. And there is one other big factor. Your mother--or somebody's mother--was always on guard to keep the floors clean and scratch free. It was pretty standard for kids to take their shoes off when you visited someone that had really nice hardwood floors.
One of the big problems today is that many people will not go through the cost or inconvenience to put down a really good oil based finish on their floors. To do it right, You want to put down a coat of poly on one day, give it a full day to dry, sand and put down another coat of poly the next day, give it a full day to dry, and then sand and put down the final coat of poly and keep everyone off for a full day after that. That means keeping the dust down and everybody off the floor for a week just for the finish. This is expensive in labor if you have all those returns by the finisher and you can find one that will do it that way at all. The same finisher can put down 3 coats of water based poly in a day and a half.
For what it's worth, I prefinished a set of stair treads with Parks Pro Finisher Oil Modified Polyurethane this way. They are beautiful and the finish will last forever. But I certainly would not have been able to do this if I had to finish the stair treads in place for the only stairs to the second floor.