Why does Gohan train with Picollo instead of Goku?

Goku isn't always away on Beerus planet as he has to be a farmer and provide for his family. Why doesn't Gohan train with his dad. His greatest power development via training came with Goku in the time chamber. Picollo is limited in terms of power and can only help Gohan so much. Training with his GOD tier Father would help Gohan grow by leaps and bounds plus his Dad is a fighting Genius.