Why are there no good effects of sincere repentance (Istighfar) evident in someone who frequently engages in it?

The lack of apparent effect from seeking forgiveness (Istighfar) may be due to a defect in it, such as restricting it to the tongue without sincerity of intention and a submissive heart. The good fruits of seeking forgiveness are realized when it is accompanied by a submissive heart and sincere will. It is preferable to increase seeking forgiveness during the pre-dawn hours (As-har), as mentioned in His (Allah's) saying: "And those who seek forgiveness in the pre-dawn hours" and "And in the pre-dawn hours they seek forgiveness." Seeking forgiveness is like supplication (Du'a); the attainment of its fruits depends on the fulfillment of conditions and the absence of impediments.