I think there are at least two other reasons, too:

One, sweat equity matters. I know I value pieces of furniture I built myself more than furniture I bought, even though the furniture I bought is better quality - because what I made myself represents my skill and my labor and my commitment. And in a throwaway culture, creating that emotional commitment to clothing or furniture or a home matters.

And two, rammed earth tires require no supply lines, no 3D printers, no expensive tools or complex chemistry, no gas or electricity, even. Just used tires, local dirt, and local labor. If global supply chains fall apart and resources get scarce, people can still build Earthships - and the people who are building them now will be able to teach others how to build them in the future.

They are also generally free or very cheap if you are willing to haul them away.

As i understand it though, the labor intensity of the overall build makes the earthship just as expensive, if not more so to build than conventional housing, even modern eco housing. You really only save money if you put in the thousands of hours of work yourself or with volunteers.

Ive always wanted to do it, but it's a serious commitment that may not make actual sense anymore.