"They" are doing it! Remarkably, more than half of new energy generation deployed in the United States this year has been from solar. It's arguably the most shovel-ready form of energy infrastructure that exists right now.
Your framework is bizarre in the extreme. Despite the fact that no one thinks of mirror plants as having anything to do with the future of PV generation, you treat the future of all solar as if it hinges on that consideration. Meanwhile, back in reality, solar power could realistically occupy up to 30% of the grid's energy generation capacity without intermittency becoming a deal breaker. Combine that with the fact that the grid itself is going to continue to grow, and so 30% of whatever that future amount of total generation capacity is going to be a rather extraordinarily high number, solar is going to be an exceptionally important part of the energy generation picture in the future even if we never made an inch of progress on solving the intermittency problem. For that matter, it seems infinitely more rational to think that what's actually going to happen is some degree of experimenting with energy storage, more sophisticated demand management, and perhaps partner technologies that ease the stress of base load and peaking responsibilities. But instead of that, you're doing this completely out of left field U-turn towards solar mirrors.
So again, it's bizarre in the extreme to take that picture, which is about billions of dollars of grid infrastructure and multiple Terawatts of energy, and swap that out for a hypothetical relating to mirror plants, which is never going to happen in which no one is seriously entertaining, and to treat that question like it's decisive about the fate of solar power in the future.
This is what I mean about people coming out of the woodwork and treating big picture energy questions like they hinge on these bizarre idiosyncratic hypotheticals that have nothing to do with anything.