Unfortunately much of Phoenix is covered with a hard layer of soil known as caliche that is expensive to dig through, meaning that most houses don’t even have basements. But if it saves a lot of money on cooling it might be worth it.
Developers don't care about cost of operation, only cost to build. If there weren't efficiency rules in building codes developers would still be building houses with paper walls here for $750K.
Wonder if adding ~8 feet (a typical basement dig depth) of fill could be less expensive? After basement floor is built? Perhaps a development could be planned around this. Or, the lower floor of entire neighborhoods could be turned into basements, with stories added as desired. Areas of cities have been raised in similar manner, for different reasons, eg after a flood in Sacramento, after a fire in Seattle.
Burying a basement layer above existing grade is interesting. I hadn’t considered the possibility of backfill to create more thermal mass but it makes sense to me. It would require importing a fair amount of material though. I would need to understand where that material comes from and the overall impact it would have to do it at scale.