There are billionaires worth over $100 billion, and even more worth between $10 billion and $100 billion. So why haven't any of them bought most of the bitcoins? They could have done so, for example, in 2020, when the price of bitcoin was $5,000-$8,000. Bitcoin's market cap is now less than $2 trillion, and it used to be even less. Some multi-billionaire could have bought at least 10% of all bitcoins, but why hasn't anyone done so?
We don't know for sure, maybe some of the millionaires-billionaires have already bought bitcoin, and we don't even know anything about it. They don't need to count in front of others. This purchase may not have been direct.
And anyway, why did you start this conversation? Did you want the billionaires to pump the price of bitcoin with their purchases?
Also, the level of trust of billionaires in bitcoin remains unknown. It is possible that they were afraid to invest in this asset due to high risks (in their opinion) in 2020. This is now, when the price of $100k seems obvious, but then, 5 years ago, few (nobody) could imagine that the price would grow from $5-8k to $ 100k. I hope that billionaires are now biting their elbows from lost profits, and they will have to buy bitcoin from small holders at the current inflated price.