Because nowhere in the Bible can you find anyone calling Him that.
I think people call him ‘Papa Jesus’ because they are trying to describe a relationship that feels warm and relatable. I understand the point. Still, the Bible doesn’t call him Papa Jesus and the reason is theological. Jesus is the Son, not the Father. Calling him Papa is not consistent with what the Bible teaches about the Trinity.
Jojo Agot 
I strongly agree with your thoughts on this… good expression and background info… and this kinda reminds me of the unbiblical term, “mother of God”… i am now thinking that we ought to be more careful of the names we use to address God..!
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Hi Snow, thanks for dropping by. Mother of Jesus is a more precise term. 🙂
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Jesus is single
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Hi. So we should not say or call Jesus Papa Jesus and Mary Mama Mary? I am a catholic since birth and most of our catholic priests says Mama Mary and Papa Jesus. For my knowledge we use this because they are our heavenly spiritual father and mother. And God is in 3 persona The Father The Son and the Holy Spirit. We sometimes use Papa God. God bless us all. 🙏☝️💖
Just saying. No hating or arguments please. Thank you. Peace to us all and the whole world Amen! 🙏🙏🙏
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I believe we should stick to what the Bible actually says.
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When we say God, it is the father of Jesus, and nobody see God only Jesus, Jesus have the Three Persona not God. Just make the long answer short. God is the Father, Son is Jesus and the Mother is Mary. Then, son will never be called father UNLESS he have son. then who is the God are you talking about? God or Jesus? just to be clear. God is a God, then Jesus is a God too, look for John 10:30 “I and the Father are one.”
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