Because bad actors like fossil fuel and car companies will say "look, the government is funding fusion. Don't make us go renewable now, just wait five years until fusion is here." You have to consider the political impacts pursuing research will have on society's perceptions. Even if you know your project is just a wild experiment that probably won't work, journalists won't.

They already do this fyi. Solar plants tend to use mirrors that concentrate light to heat water and turn a turbine instead of actual solar panels. Amazingly, iirc converting light into heat, the heat into steam, and then the steam into kinetic energy, is still more efficient than a normal photovoltaic cells.

The concept is viable. Just needs moar mirrors