[dsr_]

It is partially learned, partially a built-up tolerance.

Anecdata: About three years ago I drastically reduced my intake of carbohydrates, including all forms of sugar and starch. After around two months, I tried tasting some things that I had stopped eating -- fruit juice, a bit of pie -- and discovered that they were horribly sweet to my tongue.

[stcredzero]

The amount of sugar going into foods has increased. I remember there being around 20 grams of sugar in most sodas. Now, there is typically about twice that amount, and Honest Teas are "lower in sugar" with 19 grams. The US food industry's tactic is this: foist lots of sugar on people when they're kids and don't know any better. Then, when they're adults, you can get away with plying them with lots of high fructose corn syrup, which is super cheap due to subsidies.