What made this historic retard in Buddhist Pagoda between Shilla Dynasty and Koryeo Dynasty

I don't know how I could explain this phenomenon.

Let's look at the pagoda and compare each other.

At first Shilla dynasty style. Below was the pagoda of Soo Deok Sa.
Actually the pagoda of Soo Deok Sa was estimated as an early work of Koryeo dynasty which was strongly influenced from Shilla dynasty. The pagoda of Shilla dynasty is much more beautiful and well balanced than that of early works of Goryeo dyanasty.