It matters to the people running those companies (Because they own a lot of stock, or work for people who own a lot of stock). It matters less for the firms, themselves.
A high stock price prevents a corporate takeover (which is not a real-world-value-destroying activity - factories operated by a company don't burn up when it happens), and it makes it possible for the firm to raise money by selling stock. In a world of low interest rates, and easy credit, this is not very important.
