If you're older I think some of this is obvious. Biggest example for me is grapefruit, they used to be barely sweet, when I was a kid they were mostly bitter and we used to add sugar to them, now they're always extremely sweet.
This may differ based on location, as my grapefruit (non organic normal supermarket bought) are still quite bitter. I'm located in Europe so these might be Spanish grapefruit, though not sure.
Your palette changes pretty significantly over time, especially between childhood and adulthood. Grapefruit may not have changed at all, and you might still find them sweeter at 30 than you did at 8.
My parents' generation used to add sugar to everything because they considered sugar a source of energy.
I remember eating strawberries directly from the plant, and they were sweet. However, my aunt would serve the same strawberries with sugar as an afternoon snack.
