Billionaires are buying a huge share of Bitcoin, it's just not noticeable because they do this strategically usually with OTC (over-the-counter) trades to prevent buying at premiums in spot markets.
To elaborate, for a billionaire to be able to buy Bitcoin responsibly (which they almost always do), they have the option to:
- Spread their funds across exchanges to be able to buy from the order book gradually (requires a lot more time, patience and trust in multiple custodians)
- Conduct trades over-the-counter (OTC) trades, which are off-market trades that don't generally effect the spot price.
It's more attractive for billionaires to accumulate with OTC trades in comparison to if they were to buy directly from an exchange.
If you're wondering something like "What if a billionaire already had a lot of Bitcoin, wouldn't they want to buy a lot of it on-market to push the price up?", the answer is that Bitcoin's market cap is over $2 trillion. It would require a lot of buying power and strategic execution across international exchanges to make this happen, and it's a gamble that it would work to begin with. It would be similar to saying "What if a billionaire had a lot of silver, wouldn't they want to buy a lot of it on-market to push the price up?" (I use silver as an example because its market cap is similar to Bitcoin, around $2 trillion). The answer to both is that, if it could be done, it would be done (or maybe, it already has been done, and maybe, it might happen again!

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