It could be that “Most
dugout homes are excavated into hillsides rather than dug from shafts” from your second article. AFAIK temperature doesn’t get cooler underground. https://en.wikipedia.org/wiki/Geothermal_gradient
Hi, I'm in actual geophysics .. and you're linking to a phenomenon (quick, read your own link) that occurs over a scale of tens, hundreds, and thousands of kilometers.
Near surface underground is different.
Aquifers and all manner of other things behave differently to your blanket "AFAIK temperature doesn’t get cooler underground" and it's well known in practice that digging down a few stories evens out the tempreture compared to above ground.
This even works as a cheap passive cooling system for data centers:
data center was the original reason for my buried wall: the computers were going to live on that wall and shed their heat into it. Big heatsink. Worked well for a couple years and then AT&T decided to take away my bandwidth, so i had no more excuse to have 10kw of racks running.
Near surface underground is different.
Aquifers and all manner of other things behave differently to your blanket "AFAIK temperature doesn’t get cooler underground" and it's well known in practice that digging down a few stories evens out the tempreture compared to above ground.
This even works as a cheap passive cooling system for data centers:
https://pawsey.org.au/groundwater-cooling-system/