There are a lot fewer bespoke parts than you might think. Creating new molds is expensive and if you look closer you'll see that odd shapes are reused for different purposes in different sets.
For some firsthand examples, I have a few of the "botanical" sets, and they have things like Technic wing/fin pieces for leaves, flowers made out of car hoods and trunks, and pink frogs used en masse for cherry blossoms.
They're very creative at reusing pieces. One of the Lego Mario sets has a bomb on a parachute, but the parachute is made out of a white version of the old 3-flower-stem piece.