On the basis of sound economic argumentation, this gives the primary objective a constitutional status. Acting as sovereign bodies, the legislatures - but, of course, not the central bank - took a conscious decision to protect the mandate for monetary policy, namely price stability, from the influence of short-term political considerations, such as changes in government or upcoming elections.
Of course, in principle nothing is set in stone for eternity. The objective for monetary policy could also be changed. A democratic procedure for such a change exists, namely an amendment of the Treaty. This is a constitutional process similar to that which originally set the mandate which requires approval by the legislatures of all Member States.