Why folding camera?

I don't know much about optical science, but from years of taking pictures with many cameras, I can tell the differents between good lens and bad ones.
Firstly, I impress with the classic look of them. Secondly, I was amazed by the design of machanics and size while folded. Lastly the optics quality of these older lens, mostly it has around 10 blades of diaphragm which produce smooth completed circle to out of focus spots (circle of confusion). The color saturation, sharpness, contrast and toning of the pictures maybe different from lens produced in these days, but the unique characteristics of the older days lens give different feeling, even use with modern films.

Folding camera history, in short
I think folding cameras era begined around early 1900s (maybe 1920s or 1930s), but of those what I saw and still working today they're 1930s or later. I've only 2 brands of folding cameras in my collection, which are :

Zeiss and
Both were made in German and had produced many kinds of cameras and accessories :

and divided roughly (by me) into 4 eras :