Why does conscience reproach after a sin, not before it?

Satan beautifies disobedience for a person and conceals its consequences from him until he falls into it, then he abandons him. Allah Almighty has shown Satan's beautification of evil deeds in several verses. Then Satan disavows those whom he misled after they commit disobedience, as in His (Allah's) saying: "Like Satan when he says to man, 'Disbelieve.' But when he disbelieves, he says, 'Indeed, I am disassociated from you'." However, after committing a sin, a person returns to his true nature and regrets his action, and Allah may erase the sin of disobedience through this regret. It should be noted that Satan's temptation does not affect the pious; they remember and repent if they are touched by a passing thought from Satan, as Allah Almighty said: "Indeed, those who fear Allah - when an impulse from Satan touches them, they remember [Him] and at once they have insight."