God simply means deity.   It is not a personal name of anyone specifically.   

Jesus is a person.   He exists.   I say He exists because He lived among us and, though He died, He raised Himself from the dead and was seen to ascend into heaven.   

Christians call themselves Christians.   To be a Christian means that
   → you believe that God came and dwelt among us
   → you believe that Jesus is divine
   → you believe that Jesus is Saviour
   → you believe that Jesus is Lord
   → you believe that Jesus has all power
   → you believe that Jesus will judge the quick and the dead

So, why talk about or to God as if He exists apart from Jesus?   

Your answer may be
   → because Jesus told us to pray to our Heavenly Father
   → because He said His Father was greater than Him
   → because He said He was going to His Father.   

The question is: "Who is His Father?"

The answer is profound and unifying, undermining the concept of the Trinity.   

The Holy Spirit is the Father of Jesus.   

But Jesus said He and His Father are One.   How can that be?   

The Holy Spirit who is God is the Spirit Of Christ Jesus.   

Jesus is Spirit Soul And Body just as we who were created in His image.   

Jesus is the express image of His Holy Spirit.   

Jesus is the Incarnate Word, the Body and Soul of His Holy Spirit.   
So Jesus is the Body Of God and Soul Of God filled with the Spirit Of God.   

In the beginning was the Soul Of God and the Spirit Of God - two aspects of the One God.   

Jesus is the Son Of Man - God in human flesh.   

Jesus is God.   Jesus is the name of God.   

So, back to the original question: Why do Christians talk to God rather than Jesus?   

Jesus is in heaven.   His Holy Spirit is in us.   We are to fellowship with Christ via His Holy Spirit in us.   

Since humans (even Christians) have difficulty grasping the Spirit Realm, they tend to create physical entities to deal with what appears to be an inconsistency with physical laws.   

That is the rational mind at work and it invariably draws wrong conclusions outside of the Physical Realm.   

Spiritual Laws supercede Physical Laws.   

The Spirit Realm supercedes the Physical Realm.   

The Spirit Of Christ fills the universe with The Majesty being the focal point from which He eminates in heaven.   The Body Of God is now present with The Majesty.   

The Spirit Of Christ is Christ and the Body Of Christ is Christ.   The Spirit Soul And Body of the Lord Jesus Christ is God.   

After making these statements on the deity of the Lord Jesus Christ as the One and only true and living God I must draw this conclusion:

Christians refer to God as if there is some person with power or authority that exceeds that of the Lord Jesus Christ - call Him Big Daddy God or Chief Executive Officer God or whatever.   

This reflects doubt about the Lord Jesus Christ being Mighty God and Everlasting Father.   

When Jesus told us to ask the Father in His name He was telling us to address the Holy Spirit using the name Jesus.   

So, though Jesus is in heaven, His Holy Spirit is in us.   There is one name for God and it is Jesus whether you are referring to His Body or His Soul or His Spirit.   

Stop doubting who Jesus is.   Stop imagining and giving honour to another `person` who does not exist.