But if it was cash and debts instead of assets and debts, the company wouldn't be worth $300 billion to bondholders?
If you give a teller $1 for 4 quarters, you don't say that you spent $1.
I currently am worth $0 to that bondholder.
I spend one of those borrowed dollars on a chocolate bar.
Now I'm worth $1 to that bondholder??
The spending is done with a completely different person than the bondholder.
I'd love to create lots of value for you by borrowing money from you. I would even consent to not destroy any of that value through making payments.
The bond is worth $300b to the bondholders, but only because it is expected to be paid back and is secured by the $300b assets. You can prove that by assuming those assets disappeared: how much is the bond (or the company) worth to the bondholders then?
And that's assuming the company is being liquidated. Most companies with viable businesses are worth a lot more than their assets because the big part of the valuation is assumed future earnings.