This is the conclusion of the paper [1] that this article is based upon: "We suggest that any real declines are generally most easily explained by changes in cultivated varieties between 1950 and 1999, in which there may be trade-offs between yield and nutrient content." What National Geographic says scientists say, "Scientists say that the root of the problem lies in modern agricultural processes that increase crop…
My anecdote from my garden is that my smaller cucumbers have way more taste, my smaller red bellpebbers are way more pebbery, potatoes have a richer taste, if this is just freshnes i dont know, but there for sure is a huge difference.
And I am comparing to bio carrots we buy in Switzerland, so can't go much higher than that when shopping (apart from farmers markets maybe but that depends what kind of farm).
Maybe its about transport and premature harvest, like bananas - if you ever taste some in exotic locations where they harvest them in the morning, its hard to ever enjoy bleak taste of those available in western world.