The United States Government does not sell the stocks of private companies. The prices of stocks on the stock market changes as the supply and demand for stocks change. They can change at any rate, or prices can stay the same for a long time. How much they move up does not forecast how far they may fall. Stock prices will usually not fall if the company remains successful and other investments do not become more attractive.
Stock prices reflect the interests of investors.
Stock prices are set by the supply and demand for stocks. The Securities and Exchange Commission regulates the stock markets to ensure honest practices are followed and accurate information is provided to buyers and sellers of stocks. All 'good' stocks are available for sale in large quantities. Just because someone currently owns them does not prevent investors from buying the stocks. The new investor must offer a price that is attractive enough so current owners have an incentive to sell their stocks.