In this document (thats also linked in the main article) you find a great explanation to your question.

The original design used a honeycomb structure, because problems with cracking and gas permeability had been known (in the 1960s).

On the other hand it would be more labor intensive to build it in that way.

https://docs.google.com/document/d/1ddi792xdfNXcBwF8qpDUxmZz...