Warren has over $100B invested in public equities (stocks). He’s s believer in concentrated portfolios, ie he doesn’t want to own more than a few stocks st a time. If he can’t buy $10B worth of a stock he’s not interested.

There isn’t a stock in the world you can buy even $1B of in a day without driving it’s price up dramatically yourself. So Buffett has to slowly accumulate a position over weeks and months.