First: because the Prophet ﷺ made the ruling contingent upon it, and we have no right to go beyond the limit set by the Messenger ﷺ.
Second: when the seller pollinates it, he has performed work upon it that improves it, and his interest becomes attached to it. This is unlike the case when he has not pollinated it, for then he has done nothing to it.
Accordingly, the correct view is that if he sells date palms whose spathes have split open before he has pollinated them, the fruit belongs to the buyer; but if he has pollinated them, it belongs to the seller.
If he pollinates one palm but not another, each has its own ruling: the fruit of the pollinated palm belongs to the seller, while the fruit of the unpollinated palm belongs to the buyer.
If he pollinates part of a single palm—because, as is actually the case, the spathes may not all develop evenly—the fruit belongs to the seller, giving precedence to pollination. This is because it is well known that it was not possible to pollinate all the clusters of a palm except in these recent years in our country. Previously, they would pollinate them all: after the first ones split open, they would wait a little, then open the smaller ones before they split open, thereby sparing themselves repeated climbing up and down the palm. In earlier times, when people were active and had leisure, a person could climb the palm several times, pollinating the first fruit, the middle, and the last.
If someone asks: Why did some of the jurists, may Allah have mercy on them, depart from pollination and instead make the ruling dependent upon the splitting open of the spathe?
They say: Because the splitting open is the cause of pollination; thus, the Prophet ﷺ made the ruling contingent upon pollination, while what was intended was its cause.
It is then said: What evidence is there that this was what the Messenger ﷺ intended?