# If a constant current can create constant magnetic field , why do we need changing magnetic field to induce current?

One answer to your why, is, because that is what Maxwell's equations say, and they model perfectly the data we have of classical electromagnetic interactions.

Particularly the form :

$$ \nabla\times E = -\frac{\partial B}{\partial t}, \;\;\text{Faraday's induction law} $$

The change in the electric field in space is affected by the change in the magnetic field in time. As current happens only when there is transfer of electric charge, if the time derivative is zero then the electric field that could move electrons or ions to generate a current, would be zero.

Note that it is a law, i.e an axiomatic statement, derived from observing data.