So, why not cigarette adapter DC sockets?
To supply 10x the current, you need substantially larger wires. Wires are heavy. Airlines don't like heavy, it costs a lot of money over the lifetime of an aircraft to haul non-fare paying weight around.
Another point, 12vDC is not a typical aircraft voltage, so a DC-DC converter would be needed to generate the 12vDC. 12vDC is typically not a native laptop input voltage (19vDC is more typical), so another DC-DC converter would be needed. At that point, an inverter (DC-AC) and normal laptop power supply (AC-DC switcher) makes more sense (efficiencies are similar).
There are DC adapter plugins in aircraft - the idea is that they are only sold for laptops and are expensive enough that few people use the.
I don't use it very often because all the cords that it would require annoys me, and my laptop has 12 hours of battery life. But it is there, leading me to believe that this is not actually a problem.
(I think the fact that it's DC power limits the number of people that will use it, because you have to plan ahead, and nobody ever plans ahead for flights except seasoned travelers. If it was AC power, people would plug stuff in just for the hell of it, instead of reading a book as they do now.)
I am not familiar with any specific methods of causing a large explosion that access to a 120V AC socket would allow, which not having access to one would not, with what is currently allowed to passengers through airport security [0]; But considering that producing a cigarette lighter or some nail polish remover in the cabin are grounds to be tackled by an air marshal and prosecuted, an electrical outlet is a hell of a lot of accessible power.
[0] kindly disregard my past five minutes' search history, NSA sniffer