Because they've been trying to get that far for decades, and failed until now. It wasn't that long ago that people were saying we'd never figure it out.

Basically, this kind of energy, that powers our sun and all the stars, and does so in ways that are much cheaper and easier to keep safe than today's fission reactors, it was a question if we'd ever be able to harness and produce that energy ourselves here on earth. This pretty much proves we can, for the first time.