There are two main ways to buy a public company. One way is to make a deal with the board of directors which gets ratified by the shareholders in a vote. Becaus

There are two main ways to buy a public company. One way is to make a deal with the board of directors which gets ratified by the shareholders in a vote. Because stocks are highly liquid you really have to offer a premium over the current stock price for that to be a good deal for everyone involved. Then think about what happens after the board agrees to the sale, people can still trade their stocks on the open market, but it'll be a vastly different landscape than normal because those stocks now have a fixed price at a future date. So it doesn't make sense to buy stocks at higher than that price, it also doesn't make much sense to sell stocks at lower than that price unless you need liquidity now. The other way is to just buy up a majority of the public, voting shares, typically called a hostile takeover. This is the hard way, and can become extremely expensive if enough people decide they don't want to part with their shares except at very high prices. As you buy up shares the price will go up, so it ends up being a longer, more difficult, less certain, and more contentious way to buy a company.