Because that's exactly how many parts of the NT present the situation:
Acts 2:22 Fellow Israelites, listen to this: Jesus of Nazareth was a man accredited by God to you by miracles, wonders and signs, which God did among you through him, as you yourselves know.
If what the writer of Acts really meant to say was that Jesus was himself God, that sure is a funny way of putting it.
Even in the gospel of John with its high Christology this is spelled out:
John 5:36 "I have testimony weightier than that of John. For the works that the Father has given me to finish--the very works that I am doing--testify that the Father has sent me.
John 13:16 Very truly I tell you, no servant is greater than his master, nor is a messenger greater than the one who sent him.