Why are the floors of the buildings on Marunouchi Nakadori Street Nakadori made of wood?

When Marunouchi was sold off by the national government, the city ordinance required that the buildings be fireproof, and so the floors of the buildings should have been fireproof to prevent fires from spreading from the lower floors. However, for some reason, only the floors of buildings 6 to 11 and 14 to 17, which face Marunouchi Nakadori Street, are made of wood.

The floors of the buildings on Babasaki-dori, including Building 1, which was completed in 1894, were specified as "fireproof floors," and the "Wayo Kairyo Dai Kenchikugaku" (Great Architecture of Way and Western Improvement), published in 1904, also describes them as "fireproof floors," so the difference is not a technical issue. On the other hand, the buildings on Babasaki-dori, which have "fireproof floors" and "fireproof floors," are three stories tall, while Buildings 6 to 11, which have "wooden floors," are two stories tall, suggesting that the difference in structure was due to scale. Of these, Buildings 6 and 7 were originally planned as apartments and were changed to rental offices shortly before completion, but as the floors remained wooden, it is thought that the difference was not due to purpose.

Therefore, the city ordinance required that buildings be fireproof, but it must have required only buildings over three stories to be fireproof, or the concept of roadside fireproofing already existed, and only buildings facing major streets such as Babasaki-dori were required to be fireproof... (?)