Why did God decree the world should be taxed at the time of Christ’s birth?

The usual reason given why a sovereign God ordained a decree to tax the world was to get Mary to Bethlehem to be born in the prophesied location. Really?
This explanation to me is lacking. God had already proven that He was able to talk with both Mary and Joseph and that they were willing servants. If He merely wanted to get Mary to Bethlehem to fulfill Micah 5:2, He could have told them. But if that is what happened, something would be lacking.
Imagine the story without the decree. Mary and Joseph travel to Bethlehem where no crowd would force them to bed in a stable. Surely some relative would welcome them. After all, the main use of the word “inn” is a guest room. This would have made it tactically difficult for the shepherds to visit the baby that night, or even to find him since they couldn’t do a house search for a baby wrapped in swaddling clothes.
Further, God’s plan often is to bring a group of people together to hear a message, then spread them out to share it with others. He does this weekly in the design of the local church. He did it at Pentecost where people from 16 nations heard Peter’s sermon. When those who received the message returned home, it gave a kick start to the church age!
In Bethlehem were Jews from all over the country there to register for the taxing. We are told that, when the shepherds had seen the baby, “they made known abroad the saying which was told them concerning this child.” The entire nation should have been stirred at the news that God was on the move and the fulfillment of His promise of redemption was underway.