I think it is due to expense.  A quality A/C system would allow one to add refrigerant as opposed to having to replace the unit or try sweating on a vampiric tap (which eventually will leak.)  A quality A/C system would be engineered so the noise compressor and other parts would be as isolated from the inside as possible, and it would be able to sense a low voltage and not fire up the compressor as opposed to allowing it to burn out.
There are Youtube videos of people running small 5000 BTU/hour A/Cs from a solar array and four deep cycle batteries.  A standard 13.5k BTU/hour unit or a 15k BTU/hour unit, this would be very tough, but a small A/C unit with a low duty cycle, this is likely doable for a couple hours.