Why permanent magnets are made up of steels and core of soft iron is made up of soft iron?

An alternating current passes through the primary coil. The alternating current produces a magnetic field that continuously changes direction. The soft iron core increases the strength of the magnetic field. So the transforemer is made of soft iron core.

Retentivity of soft iron is greater than retentivity of steel

soft iron is more magnetised than steel loses its magnetism more rapidly than steel