If the visible frame of a sofa is cut full of holes, something else has to be holding the sofa up. On this one, it is a second frame you never see.
The openwork you are looking at is a shell. Carved scrolls with air between them cannot carry the load of three people and years of use - the material is simply not continuous enough, and any single bridge of wood between two voids would be doing work it was never sized for.
So the sofa is built twice. Inside, a plain structural frame in solid teak takes the seat load, the arm load and the racking that comes from people dropping into one end. Its rails are square, its joints are conventional, and it is entirely hidden. The carved openwork is then made as a separate assembly and jointed onto that structure, positioned so the shell is carried by the frame rather than the other way round.
It doubles the joinery in the piece and it is invisible in the finished sofa. It is also the only honest way to make carving this open, and the reason we are willing to warrant the frame for twenty years.