Side walls get in the path

P2PPCB covered style keyboards have frames like this:

The cover consists the side wall and the bottom. The frame is top only. However in common sense, top side part should consist almost everything, and the bottom side is just a lid to avoid dust. Why P2PPCB covered style keyboards become like this?

The answer is component insertion path and tool path. Contact-to-socket asssembly should be inserted to a hole through a path, and single IDC contact press tool should reach the contact through a path. The video below shows the pathes by green solid:

Not frames but covers should have walls to make assembly easy.