Bava Metzia 119 - The Law is Like Rabbi Shimon

In the case of vegetables growing out of the vertical wall between two gardens, why does Rabbi Shimon says that the reach of the upper garden's owner's hand determines to whom the vegetables belong?

In principle, Rabbi Shimon agrees with Rabbi Meir's view, that the vegetables belong to the owner of the upper garden because they are growing out of his earth. Rabbi Shimon, however, maintains that the upper owner abandons any vegetables that he cannot reach. Since he would have to go through his neighbor's garden in order to pick the vegetables and it would be embarrassing for him to ask his neighbor's permission to do so, it is is assumed that he relinquishes them to his neighbor.
They reported Rabbi Shimon's ruling to the Persian King Shapur, and he said in praise of it, "We extend our graciousness to Rabbi Shimon."