Your question is basically, "Why not <certain property norms>?"

What kind of answer are you expecting? Because other property norms are better. Because the ones you advocate would lead to one person getting an undeserved bonus for very little work, and the other being sexually exploited.

The person who picked the coconuts does have a right to the value of their labor, yes. But the value of their labor has just been cut in half thanks the arrival of a competitor on the coconut picking market.

There wasn't anyone to contest their ownership of the coconut trees before, but now there is. That claim now has to be satisfied.

Why not? Because we can do better. What other reason is there?