“By 2046, a 100MW fusion plant will be in operation and selling electricity to the grid.”

The reason is simple: money. Or capital, if you prefer. Capital gets things done, and now, capital is interested in getting fusion done. Between General Fusion, TAE (formerly Tri-Alpha Energy), Commonwealth, Hellion, and others, there is massive funding moving into commercial fusion. Very likely, most of them will fail to reach unity. But I think it is also likely that at least one of them will succeed. And once one does, capital will do what IT does, and start extracting return on its investment, which means rapidly scaling and deploying. Commercial fusion is closer than fusion-skeptic academics like to acknowledge. Yes, there have been delays, but the progress is orders of magnitude faster than we have seen at ITER. And everyone knows the NIF is a weapons program, not an energy research. Commercial fusion startups are (ahem) laser-focused on producing a working fusion plant, within a timetable that provides their investors a reasonable return on investment. I think at least one will succeed within the next 25 years.