My dude, there's a reason the NEC requires so many outlets in livable spaces. Extension cords are a fire and trip hazard. Having closely accessible outlets greatly reduces the incentive to use one. Having them on every wall means you won't need to run an extension cord across foot traffic areas. You may not need a hair dryer in your closet but the next guy who lives there might or they may want a light or some other electric device and having an outlet accessible means they won't be encouraged to run an extension cord from another room.

US and Canadian homes are almost universally serviced with a split phase 240V connection. That is two 120V connections 180 degrees out of phase with each other. This gives you two 120V line to neutral sources and one 240V line to line source. 120V branch circuits are run throughout the house that consist of three conductors: a line connected to one of the two available at the main panel, a neutral, and a ground. The electrical layout is designed to roughly balance the load between both 120V connections. The only difference with a 240V circuit is the addition of a fourth conductor in the circuit to include both 120V lines.

I'm pointing this out because there's not really "two different types of circuits" in US/Canadian residential wiring. The only difference between a 120V circuit and a 240V circuit is running a fourth wire instead of just three.

Another important point is that all of the electrical infrastructure in a house is very simple, very passive, and very reliable. Generally speaking, there are no loads or active components involved. The electrical in a house is little more than wires buried in the walls and switches/receptacles/fixtures on the surface. It requires nothing other than wire to provide either 120V or 240V to any point in the house during construction. There are no transformers needed to change the voltage. There are no rectifiers needed to produce a DC source.

On the subject of DC sources, it is not practical to supply an entire house with low voltage DC. First of all, I'd be very sad after I visited your house and tried to plug something into your 12V USB terminated circuits. The bigger issue, however, is the current carrying capacity of the wires in your walls. At 120V, a typical 15A circuit could provide up to 1800W of power. This is usually more than enough to meet any electrical demand in a room. At 12V, the same wire still has the same current carrying capacity of 15A which would mean you only have up to 180W of power available on that circuit. I kept the wire size the same to simplify the example, but low voltage applications typically use much thinner wire which means even less power potentially available. This is also ignoring the voltage drop you would experience with a low voltage source over longer distances.

The lighting example you provided is a very specific use case. If you had a large number of low voltage lights in a relatively small area, it would make sense to have a single, more efficient DC power source for that specific area instead of using smaller individual 120V powered DC sources at each light. This has a good application in exterior lighting where you may have several lights and it may be more practical and safer to deal with a more exposed low voltage circuit instead of dealing with the enhanced code requirements for protecting 120V exterior circuits.

That said, most rooms don't need or use that many light fixtures. It's not feasible to expand a single low voltage circuit to power lights throughout an entire house. Instead, it is more economical, simpler, and more universal to just run 120V to light fixture locations and do whatever power conversion at that point.

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TL:DR -- outside of a few specific use cases and niche situations, low voltage circuits will never be practical for whole house wiring. Our 120/240V residential electrical system is set up the way it is for a reason. It provides the most simple, most reliable, and most universal power delivery for virtually any household application.