I could be wrong but I think you could get started with all of that with a fraction of $1B.

Sure there is leisure and entertainment but if you want to use it to do something meaningful, with only 24 hours in a day you'll probably have much more money than time to use it well.

On the other hand 1B is really an arbitrary choice of number, so I think the reason he would choose this specific number definitely has more to do with arbitrary reasons (class, status), perhaps subconciously.

Personally I don't agree with the parent that everyone wants that much money. I think I can safely say not only am I content with much less but I also don't ever want to have the responsibility of having to manage that. Though I'm already saying that from a place of privilege where I don't need to worry about survival.

Furthermore, a lot of money almost certainly places you in an outlier group where normal laws and rights as formulated by humans don't apply the same. Assuming everyone has some empathy and sense of justice/righteousness, that should make them intrinsically not want to be in that group.