Some of that perceived value is the (wonderful) original Modernist attributes of simplicity, manufacturability, and form-follows-function, which are integral to the design philosophy of those homes.

The design work of the Eamses is another case: https://www.vitra.com/en-me/magazine/details/eames-potato-ch..., it’s just a magnificent use of the material.

Even the original Case Study homes were intended to be affordable, not made as mansions: https://en.wikipedia.org/wiki/Case_Study_Houses (https://en.wikipedia.org/wiki/Bailey_House_(Los_Angeles)#Des...)

Needless to say, I think OP is just not well informed about design.

Just as it might have been hard to make an ornate street lamp, it’s also hard to make a clean modernist home. There are reasons (personal, practical, philosophical) to prefer one or the other for a given use, but the author isn’t seeing those nuances.