A bigger percentage of a less valuable company, because buying the shares back costs money. Ignoring taxes and other “minor” details (like a discount applied go cash that could be “wasted”), if a company market cap is $10bn and it has $1bn in cash after a buyback investors in aggregate would still have $10bn after the cash is used to repurchase 10% of shares: $1bn in cash and $9bn in stock trading at the same price as before (there are 10% fewer shares, but the company is worth 10% less).