God valley was just a random chain of events
The entire thing literally only started because Ginny, a random 6 year old Slave girl told the Pirate world that All the big CDs were there that day
Harald didn’t eat the Legendary DF as part of Rocks’ big plan so by GV his big plan had already fallen apart.
In chapter 1096 the Rocks pirates call the God valley fight their final battle, but they also already know that Harald has broken Rock’s plan since they all know that Harald needs to eat the fruit
So it’s like a farewell battle. The Rocks pirates had decided to disband since the Harald plan had collapsed by God valley. In their last Farewell mission, they decided that Saving their Treasure, Shakky, was a good enough “final battle”
Roger arrived on God Valley salty about Rocks having taken Shakky so he just went to god valley to goon and try and take Shakky from Rocks (he might not even have know that Shakky was kidnapped by CDs)
Garp went to God valley just for Roger.
And then I’m sure when the Celestial dragons and their slaves got involved, I’m sure people’s motivations changed mid God valley war