Stacking requires stairs, and many stacked villas have stairs outside. If it rains, it will be embarrassing. If there are old people at home, folding is not so valuable. There is direct sunlight on the roof, and it will be very hot in summer. Heat dissipation is fast in winter, and it will be colder.
If the distance between buildings is relatively small, the lighting conditions of the next stack will be poor. And close to the ground, it will be humid. Another disadvantage is that it will be affected by overlap.