Because we are, why do you not understand that? It is clear even using the accounting term reckon that someone's righteous is imputed. One column sin, on the other righteous ness. The only person who wiped out sin is Jesus.Why do you keep on insisting that we are imputed with someone's righteousness when scripture doesn't say anything about being imputed with anyone's righteousness?
Scripture must be read as a whole.
1 Cor 1:30
But by His doing you are in Christ Jesus, who became to us wisdom from God, and righteousness and sanctification, and redemption,
2 Cor 5:21
He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him.
Matt 6:33
But seek first His kingdom and His righteousness, and all these things will be added to you.