The main reason is stiffness—off the top of my head, it’s roughly a quarter as stiff as typical steel, so it needs significant engineering and often much more r

The main reason is stiffness—off the top of my head, it’s roughly a quarter as stiff as typical steel, so it needs significant engineering and often much more reinforcement to keep the concrete within allowable deformation limits. Basalt and carbon fiber are more promising replacements, but are significantly more expensive.