Assuming we're not talking about private companies doing government projects, a private company will eventually run out of money if their projects fail. That's ostensibly why it's good to run certain things privately: a bunch of entities get a go at making the most popular widget and society gets the benefit of having various widgets available. The losers have their assets/staff recycled into the economy.
Companies can have more money and power than countries. There's not much keeping them from running into the same inefficiencies. Money is often secured through oligopolies that naturally occur, allowing enough money to be spent on inefficiency.
Not saying it always works.