Because it is packed with loose sharp aggregate that erodes the bond very fast. Softness of the material is not what matters - abrasiveness is. A hard bond holds the diamonds long enough to do useful work; a soft bond is stripped away before the diamonds have blunted.

It wears out in a fraction of its expected life, because its softer bond is scoured away by the loose abrasive. It is among the most common and most costly blade selection errors on road work, and the blade will appear to be cutting well right up until it is finished.

Protective segments or a wear-resistant build-up on the steel core immediately below each cutting segment. Abrasive slurry attacks the core there, eroding a groove that undermines the segment and can eventually throw it off. Its absence is what causes segment loss on blades that otherwise look serviceable.

Yes - green concrete, cut within hours of pouring before it has cured, behaves abrasively for the same reasons and takes a similar hard-bond specification. Blades are often sold as suitable for both. Fully cured concrete is a different requirement and needs a softer bond.

That needs a combination specification rather than a blade optimised for either extreme, since the two materials demand opposite bond hardness. State the full construction when specifying, as a blade chosen for the surface layer alone will either glaze in the concrete or be scoured in the asphalt.