Because of the number of failure conditions.
How could I differentiate between Rhinox being ascetic and Rhinox simply not claiming the fruit?
Assuming a tracker tracked me, how could a tracker differentiate between me fruit vending one target and visiting the other?
In both cases, there's no way to do so with me visiting Auro and Fruit Vending Rhinox, regardless of whether Rhinox receives the fruit or does not, and simply remains silent.
By fruit vending to Auro, the latter is fixed. A tracker tracking me would thus either see me visit Rhinox (in which case, he's not ascetic), or would not see me visit Rhinox (in which case, he's ascetic); the tracker would know I fruit vended to Auro because Auro would always claim the fruit.
Simple logic.