In terms of the crackpot theory I'd suspect more people ate longer stored food in 1980 than today. In terms of changes that could explain a rise in a very infrequent thing I'd suspect a lot more people eat a measurable amount of transcontinental "fresh" which probably has a lot more nutritional loss than frozen for example.
This trend is also not aligned on the timeline with a global food system where food travels long distances before it is eaten.
In terms of the crackpot theory I'd suspect more people ate longer stored food in 1980 than today. In terms of changes that could explain a rise in a very infrequent thing I'd suspect a lot more people eat a measurable amount of transcontinental "fresh" which probably has a lot more nutritional loss than frozen for example.
An awful lot of "I'd suspect."
I'll let the professional researchers work to tease it out.