Hebrews 9:22 provides the main reason Christians believe that if Jesus had not shed His blood for us, we could never have been forgiven for our sins.
I forgive people all the time without requiring that they shed blood for me. And I’m really glad that people forgive me all the time without asking that I open a vein or kill my cat for them.
God doesn’t want blood. God wants life! It is WE who think that God wants blood (when He doesn’t). The idea of God demanding blood is borrowed from pagan religions. Jesus went to the cross, not to reinforce and support this idea, but to expose and redeem it. That’s a huge idea which would take us down a whole new rabbit trail.