" But you could just use concrete which isnt expensive so its still overpriced"
Concrete is actually a lousy material from a time domain perspective. The goal of lightweight critically damped materials is clean rapid decay with low coloration. There are some implementations of using synthetic casting materials that can be cast with reinforcements to gain strength without excessive mass but the implementation of those and even concrete for that matter is a very expensive process. high precision moulds and formers are expensive to manufacture and many have only a few useable mold / de-mold cycles before they break down.
Concrete is actually a lousy material from a time domain perspective. The goal of lightweight critically damped materials is clean rapid decay with low coloration. There are some implementations of using synthetic casting materials that can be cast with reinforcements to gain strength without excessive mass but the implementation of those and even concrete for that matter is a very expensive process. high precision moulds and formers are expensive to manufacture and many have only a few useable mold / de-mold cycles before they break down.