Why weren't we sent back to heaven after Jesus was crossed for our sins ??

God's software wasn't B.C. to A.D. compliant. after several attempts at patches it sorta became an embarrassment so the project was canceled.

God's final message to all of creation: "Sorry for the inconvenience."

Hitchhikers Guide to the Galaxy

The reason, is, we have to now do our part. His part, the work on the cross, was done once for all. BUT, still, not all have responded to God after that fact. Some are still just finding out what Jesus did to save their soul from its current situation. God does not want to send people to heaven that don't want to go, or that don't believe in him, or reject him outright. He leaves the ball in our court, to decide or not. So, it is his love, that is patient, and willing that none should perish, and he waits for us. Its risky to wait ,but luckily, its not too late now.

This is a good question. The reason is because it is now our job to spread the Gospel of Jesus Christ.

Because heaven sucks, y does everyone want to go there?

we are sent to heaven only when god wants us to go not due to our own wishes .

i dont think that jesus tells us. nor his apostles