The point is to emphasize that Jesus has a divine (as well as human) nature.
It's as simple as that.
But it doesn't emphasize that Jesus has a divine nature because the name of JESUS is completely removed from the equation.
All that's left is reference to Mary and God.
It can't emphasize anything about Jesus when He isn't even named.
-— It can’t emphasize anything about Jesus when He isn’t even named. -—
If anyone knows who Mary is they know Who she gave birth to.
Theotokos is simply one of many titles given to Mary. It’s not a complete treatise on mariology or theology.