Perhaps it is for the best. I think basements are overrated anyways.
Basements were originally intended as a storage space and a space to keep utilities such as the electrical fusebox and boiler or furnace. Long ago when boilers burned coal, that was where the coal was stored.
Basements were typically dark, damp, musty cramped spaces often with access only via a hatch door. As the years progressed, the basements got bigger, concrete floors (formerly dirt) were added and other appliances made their way down there such as washing machines and on and on.
When you think about it, there is a lot that goes into properly constructing a basement for the purpose of using it as a living space.
Depending on your location (anywhere with ground frost) ideally you would need, in the worst case, piles to stop the house from heaving with the soils. Here in Winnipeg we get frost in the ground from about 48" to as deep as 72" depending on how much -40 degree weather and snow we get. We also have different types of clay soils that absorb different amounts of water so we get uneven heaving. This also leads to matters of concrete repair over the years depending on the amount of heaving one may experience. Crack repair, leaks, etc.
Then there is the matter of drainage. Ideally you would have an exterior weeping tile and an interior weeping tile system draining into a large sump pit (maintenance). There is a lot of detail that goes into building proper drainage systems and a lot of contractors do not do it properly. Concrete is much like a very solid sponge due to its porous nature. Installing carpet over concrete may not be a simple matter since if it is not properly installed, one could be setting themselves up for mold growth in the future (or simply damage to hardwoods). For example, if a basement floor was not chemically sealed but a vapour barrier was put down, there is the issue of finishinng details. Capreting usually requires tack strips that have to be nailed or screwed into the concrete floor. Once the vapour barrier is penetrated, if the penetration has not been sealed by acoustic or polyurethane caulking, there is a path for moisture to creep into the basement (albeit at a very slow rate).
Then there is the issue of Radon gas. This is a carcinogen and long term exposure has been shown to cause lung cancer. The remedy for this is proper basement sealing with products such as Xypex. If the exterior walls are properly waterprrofed then you need only worry about the basement floor. Since it is too costly to seal existing basements, they can make use of a ventilation system such as the Humidex (an exhaust fan that is intended for removing excess humidity from homes with the theory that the most humidity build up is concentrated in the basements). Since Radon gas is a heavy gas that seeps through the ground, through the pores of the concrete and settles in the basement, it can also be exhausted by means of this type of fan.
On a more simple matter, when building a new home there is the cost of excavation of a basement for new construction as well as properly preparing the foundation prior to pouring the concrete floor.
I guess in some areas you can not go up or make a home wider so down is the only place to go. The one nice thing about concrete basements is that, if at least two walls are used behind the insulated drywall of a home theater room(not to mention the concrete floor), they are two less walls that require special construction techniques to reduce sound transmission.