By taking on obscene amounts of debt for what amounts to a personal project, Elon Musk has made himself the poorest man in the world.
I think it's a striking demonstration of the perils of living above your means. If we take the definition of "poor" as the inability to pay for one's monthly upkeep, it's possible for Musk to simultaneously be the richest and the poorest person in the world.
And sure, he could always increase his investment by using more personal funds to make the interest payments, taking the longer term view (whether business or idealistic based). But the fact is that he hasn't, and has been framing this situation exactly as Twitter needing to immediately service that debt.