Why is Labor so united despite its internal left & right factions or is that just a myth?

https://preview.redd.it/82opwbnzzbah1.png?width=2122&format=png&auto=webp&s=63ef3a46542bf77179fe1408a239048123acd8a2

I have heard a lot of talk about Labor's left vs right factions. The tax reform bills passed with 90/90 Labor votes (not sure where the other 4 went), 3 independents & 1 greens member despite it being "extremely controversial". If these factions exist, what do they usually disagree on? Cultural/social issues or something else?