Sorry, but wrong. The reason it takes "years" to build new nuclear plants is regulatory, not physical. Remove the huge and ridiculous state-imposed barriers, and reactors can be built far more quickly.
"What I don't understand is why no serious effort has been undertaken to develop the technology to control the nuclear fusion reaction for use in power generation."
There has been HUGE investment in fusion research. It turns out to be REALLY DIFFICULT to initiate and control a fusion reaction outside the gravity field of a star.