Domestic intelligence obtains evidence legally to use in court although may use illegal means at times to know what evidence to collect. It's much closer to a police force. Foreign intelligence only cares about not getting caught; everything it does is illegal. Comingling domestic and foreign intellifence could produce complications because the illegal foreign activity could be exposed in court.

There's two main branches of domestic intelligence, pure domestic intelligence, such as against domestic terrorist groups, and counter-espionage, which fights foreign intelligence agencies. Those two skillsets by themselves are very different from foreign intelligence. It's like asking why a quarterback doesn't play safety.

Well not really, "electricity too cheap to meter" opens up all sorts of possibilities. Internal combustion engine transportation will be obsolete and transportation costs will collapse. The cost of running data centers collapses because refrigeration and electricity for powering computers, the major costs, becomes insignificant, so computing power will dramatically expand. Urban night will become like day with streetlights everywhere. Climate control will be available to almost all of the world population. Indoor agriculture will be feasible for most crops and worldwide hunger will be eliminated. We can expect major advances in science and technology because some scientific research is bound by the cost of energy. This just scratches the surface. Dirt cheap electricity will make changes akin to the industrial revolution.

Depends how you define "computer". An abacus is a an ancient computer as is the Antikythera mechanism.