Several thoughts, which could be used alone or in any combination:
1.) Have you thought of so-called "swamp coolers" (evaporative coolers)?
These devices work on the principle of evaporative cooling. There are 2 basic types: Direct cooling and indirect cooling. The direct cooling units are VERY simple and easy, but may result in air that is too humid to be comfortable (even though it is much cooler). The indirect is more expensive and hard (but not nearly as expensive as conventional AC), and results in drier air. Some systems use both methods: pre-cool the air via the indirect method, then run the cooled air through a direct cooler. The result is cooler and drier air than either method alone. All methods work best with very dry air (which it appears you have).
DIRECT method: Dry outside (or even inside) air is drawn through a wet screen or filter. The cooled, moist air is pumped directly inside. This method can be as simple as throwing a wet towel over a fan.
INDIRECT method: Dry outside air runs through a wet screen or filter, to get cooled, and then across a heat exchanger which. The dry air picks up moisture which cools the unit. Inside air blown into the opposite chamber of the heat exchanger is cooled, but picks up no moisture. Even this relatively complicated method is easier and very much cheaper to build (and operate) than an AC unit.
2.) The simplest way to keep things cool is to deny the sun entrance.
I had a home with a large skylight in the kitchen. Because I lived in a very temperate part of the northwestern U.S., I had no AC. In the summer I would block off the skylight totally with a very light custom-cut board lined with aluminum foil; then take it down in the fall. It made a huge difference (probably 5C in the kitchen).
You could do something similar, using greenhouse shade cloth, chimney flashing, or many other items that run the gamut of the aesthetics/functionality tradeoff.
3.) Venting the hottest air (from the top) and replacing it with cooler air will help; or you could leave that air alone and recirc the cooler lower air, to make it even cooler. In either case, forcing the air through deeply buried pipes would cool it.
The temperature of the earth, almost anywhere on Earth you would want to live, is roughly in the neighborhood of 50F (10C). You just have to dig down deep enough to access that temperature. All the desert critters know this: that is why they stay underground during the day. Even if you only want to go down two meters, you should be able to access constant temperatures of lower than 15C. Then you bury some pipes and force the air through them. The air heats the dirt, but that dirt is cooled by the surrounding dirt. Basically you are using mother earth as a heat sink.
The technology is relatively young, and not as well known to consumers as traditional heating and cooling methods. The upfront costs of a geothermal system are also higher, and there are fewer companies around with the knowledge and tools to install the systems.
In the US most homes are not built by the home owners, they are built by development companies who buy large plots of land and build as many homes as cheaply as they can on them. When they build these homes most of the products they use are "Contractor grade" (meaning cheap), so that the companies can make the maximum profit. Because of this, the builders typically will not choose a geothermal system over a more common HVAC system if the cost of the geothermal system is higher.
As for municipalities controlling a geothermal system, again this comes down to dollars and cents. If you were building a new city from the ground up this might make sense, but to retrofit a system like this would cost billions of dollars.
Hopefully as the "Green" movement marches on, geothermal and other "alternative" power sources will become more popular. And as they become more popular they will become cheaper, and the cheaper they get the more attractive they will look to average home owners and home builders.
Best Answer
Expense, complexity and serviceability are your main reasons.
In point of fact, the time you list as being "most useful" would be very unlikely to work well, as hot exterior temps requiring the use of A/C are often hotter than the coils on a freezer, so heat would not move then...the time you'd be able to really save on energy with heat pipes on a fridge is that part of the year when the heat pipe alone could cool the refrigerator or freezer from cold outside temps, rather than heating the house and then cooling the fridge/freezer inside the house. But this requires a bunch of complicated plumbing with unfamiliar constraints and simple "packaged units" that require only a power outlet, and perhaps a waterline for an icemaker tend to win in the marketplace.
If you want to get fridge/freezer heat outside and you have adequate budget, commercial units requiring a refrigeration tech to run lines between an outside compressor unit and the inside cooling unit are available. They are very rarely seen in houses due to the cost relative to a packaged unit.
The same factors affect other schemes such as using refrigeration waste heat to pre-heat water.
So, you could certainly try to apply heat pipes in your house, but that's going to require that you become comfortable designing and constructing them, or that you have so much money to hire people to do that, that the energy savings make no financial difference to you. If constructing them, you will almost certainly need a vacuum pump, and you'll need plumbing skills at the "no vacuum leaks" level.
I recommend The Tubular Thermosiphon: Variations on a Theme by GSH Lock as a good introduction to the subject if you pursue the build-your-own path. It's not too expensive as a used book.