These are just my thoughts on why he might prefer $2 billion over $10 billion.
If you search recent news and his personal tweets, it seems he loves racing— He featured in news around Flemington race, Easter race, Anzac Day race, and buying few expensive horses outside above events. Therefore, I would think getting $2 billion now and then spending time on what he likes is more preferable. Additionally, the journey to $10 billion isn't easy. To achieve that, he would likely have to spend more time in the USA, where our resources are located.
