Question

Why current flows in forward biased and don't flows in reverse biasing?

Answer 1

Hence, the free electrons and holes easily overcomes the weak opposite electric field from the depletion region and cross the depletion region. Therefore, the electric current flows in the forward biased condition.

Answer 2

Current passing through a diode can only go in one direction, called the forward direction. Current trying to flow the reverse direction is blocked. They're like the one-way valve of electronics. If the voltage across a diode is negative, no current can flow*, and the ideal diode looks like an open circuit.