I was also under the understanding that the reason why Jesus was the begotten son was because God impregnated Mary. Jesus was a direct descendant of
God where as everyone else was begotten by different parents but yet were sons and daughters by proxy because God created Adam and Eve.
And in this case, this clearly means that Mary fornicated!
I am sure that God did not use His own DNA to produce Jesus.
I think it probably had more to do with timing than anything else.
Jesus was readily accepted by people who knew his family as being one of them.
They had a hard time thinking of him as being anything special and rejected his first public claim at being the Messiah.