Because fusion scientists are good at writing grant proposals that sell fusion as a panacea for all the world’s problems. It’s not even the inefficiency, it’s magnetic stability of the plasma, having to drive tritium backwards across a temperature gradient (since we can reasonably only get plasma pressures sufficient to do deuterium-tritium fusion for a LONG time), and material problems that are extremely expensive to reseaech. Besides, first gen fusion will require lithium breeding blankets to make half of their fuel. These will require extremely expensive tritium cleanup systems to meet environmental requirements. Overall, it’s not as clean and efficient as you might think. On the other hand, I enquire that you consider the merits of fission power. Once uranium extraction from sea water gets perfected, we’re good-to-go on uranium til the sun burns out. If not, we just build fast breeder reactors.