Children are known to have much more sensitive taste buds than adults, which is why every culture has mild versions of everyday cuisines for them (I remember my mother made us traditional Japanese-style curried rice for kids, with extra milky sweet curry sauce, no heat). It's a fairly simple explanation, that people who prefer bland foods and scents are more sensitive, and experience those tastes and smells more intensely. Likewise, if our preference tends to be more bland than others', it might be because we're "supertasters"...or "supersmellers" in our case. Read more about supertasters on Wikipedia.
We so often dismiss young or bland taste, as a sign of being uncultured, but could it be that "evolved taste" has more to do with decreasing senses of taste and smell than with the inability to recognize the finer things in life?
OK - how do we explain people who think drums in rock or dance tracks are too loud? Now, there's a taste issue...j/k. ;-p