...why a company with a 4 trillion dollar market capitalization and a quarter of a trillion dollars in cash needs to borrow lass than two billion dollars from the government?
Because it's almost always better to spend someone else's money than your own. Failing that, it's almost always better to spend future money rather than current money. The "almosts" are there because the terms have to be scrutinized, but if the terms are good... you hang onto the cash and revenues you have. Having cash gives you flexibility and enables you to take better advantage of opportunities. And if you end up not needing the cash for anything, you can always invest it. This may not be the first rule of business, but it's got to be in the top ten.
It's honestly a good rule for personal finances, as well. If someone offers you a million dollar loan at 2% interest, your immediate answer should be "Can I get more"? And for more quotidian stuff, it's better to front-load income and defer expenses whenever and wherever possible. Pay bills when they're due, not when they arrive. Use a credit card and pay the balance off every month, letting you keep your money in your account for longer, interest-free. These strategies allow you to make some money by investing it, of course, but mostly it gives you flexibility if you need it. Which if you have decent savings you never should... but it's still better to have it and not need it than need it and not have it.