What distinguishes fruits which taste fruity from those which
do not? For example, apples, oranges, bananas, strawberries,
and grapes usually taste fruity when ripe, while bell peppers,
tomatoes, cucumbers, okra, olives, and squash generally do not. BRBR

It's an oversimplification, but the most obvious difference is the presence of
sugar.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)