I have observed the same phenomena. And I think a great deal of it is that the rubber and rubber-like polymer products are not of the same quality that they were in the past. I have rubber bands in this ancient office of mine on stuff from the 1970s that still look pretty good. But most of the new stuff is stiff as a board in about a year.
Same thing holds for gum erasers. Some are still good decades later, and others are shot almost before they are out of the store.
Monona Rossol