Why is the owner of the lower floor compelled to repair the retaining wall (the floor of the upper story) when the owner of the upper floor is not compelled to repair the separating wall?

Primary text

The owner of the lower floor is compelled to repair the floor structure of the upper story, even though it is exclusive property, because the apparent nature of the arrangement is that the upper floor owner possesses an established right to the continuous maintenance of the lower floor's structural walls. Therefore, the owner of the lower floor must allow what the upper owner is entitled to, which requires construction; this differs from the situation involving the shared separating wall.