AMEN - Our Lord did in fact forgive them while on the cross - but it was for that moment.
How do we know this? Because HE gave them room to repent - Acts-
He sent His Apostles again to them, but they still did not repent.
Some did, but not the ones where He said "you will die in your sin".
He gave them 40 years to repent - they still refuse and He sent the Roman Army upon them for Judgment in 70AD.
O Jerusalem, Jerusalem, the one who kills the prophets and stones those who are sent to her! How often I wanted to gather your children together, as a hen gathers her chicks under
her wings, but you were not willing! See! Your house is left to you desolate;
39for I say to you, you shall see Me no more till you say, ‘Blessed
is He who comes in the name of the Lord!’ ”
Matthew 23:37-39