Gonna be pedantic for a moment, because these ideas matter a lot.
DC is used in automobiles because it's what you get out of a battery. If you have more electrons on one side of a gap than on the other, you have a DC voltage. DC is entirely natural, AC requires a system to produce it. AC generators are more complicated than DC. AC devices are more complicated to build than DC devices. AC requires a means of stabilizing frequency in addition to voltage. DC doesn't have a frequency.
I'm not sure why you think this. Marine systems on yachts and larger commercial vessels have a combination of systems.
P=I*E (Power equals current times voltage.)
If you're using "DC" as short hand for "12vDC" then think about a 100w incandescent bulb (available for both 12vDC and 120vAC.
100w/12vDC= 8.3A 100w/48vDC=2.083A 100w/120vDC=.83A
100w/120vAC = .83A
As you can see, it's not AC or DC that determines the Amps, it is the voltage. If you stack (QTY)10 x 12vDC batteries in series (cable positive to negative one after the other until you put a load across the positive terminal of battery # one and the negative terminal of battery # ten), you get 120vDC.
Resistance is a physical characteristic of the conductor or insulator. Current is where HEAT comes from. Heat is movement. More electrons moving = more heat. More resistance, means less movement, means less heat. Put too much voltage to a small wire without a lot of resistance, you get so many electrons moving that the physical size of the wire cannot dissipate the heat to the air (a poor conductor of heat) before it melts.
High amperage applications need thick wires to dissipate heat, whether AC or DC. You get more power at lower amperage (and less heat for the same power "the ability to do work" output) with higher voltage. The load is what determines wire gauge- how much current do you intend to draw and how much power are you consuming? Your 12vDC input on your computer doesn't need 000 gauge, it's not drawing that much current.
DC voltage tends to drop off over long runs due to the wire's resistance. So does AC, but not as abruptly and it can be regenerated with transformers. DC voltage drops measurably over the distance a typical house wire might run. It's not enough to prevent using it.
I agree, and I think the only reason that most land-based homes with solar/wind power supplementing grid power don't go all-AC is because they retain great benefits of convenience in being grid-tied for heavy loading, avoid the cost of implementing a system that is capable of supporting all maximum conceivable loads, and avoid conversion costs in their appliances and end-user devices. It's a different matter to design from the bottom up for a location where grid power is not even an option.
I have built lots of electronic systems. I was just doing some wiring on my boat the other day. Both of our boats have DC systems, AC shore power inputs for AC outlets inside for user convenience, with DC outlets in the cockpit area. I am working on converting some of our user devices to 12vDC, like the tv.
One boat has a built-in on-board generator, Kohler 7.3kW gas genset, marine grade, low CO emissions, non-sparking, and currently, inoperable. We use a Honda 2kW portable plugged into the shore power input for now while I'm troubleshooting the on-board genset.