Economies of less scale may be contributing. We still use a lot of concrete; use peaked in 2006. But most of that is for roads and bridges. Cement mixers are dispatched much less often to small projects. Developers have a strong preference for putting things up quickly, not waiting for cement to cure, which is compounded by high labor costs. Steel consumption has been roughly constant since the '90s, but prices have doubled, possibly due to energy costs. GFRP rebar performs similarly to steel but generally is even more expensive (the greatest misconception about plastic is that it's "cheap"), though this may be compensated in the long run due to its high corrosion resistance. The application of reinforced concrete is more cautious than it historically was due to rebar corrosion issues, requiring more waterproofing and higher safety factors; GFRP is virtually immune to corrosion but has (correctly) been subject to intense scrutiny to hopefully avoid a similar crisis due to any unexpected failure modes.