> we just use bulk fiberglass to accomplish the exact same thing...basically identical performance

Absolutely false, but these sorts of attitudes are exactly why things take so long to propagate in construction.

Adding fiberglass fibers of any size to concrete will make only a fraction of the difference to tensile strength compared to the carbon nano tubes. With CNTs we're talking increases of something like 40% to the Young's Modulus which is significant.

The nano scale also improves the concrete's ductility. Fiberglass fibers have no effect on shrinkage, either. Fiberglass does not serve as a nucleation point for cement hydration products. The list goes on.