What’s stopping me from attacking the network by renting 51% of the stake for a few blocks?

The Ethereum market cap today is about $200bn. Theoretically, buying 51% of it would cost a stunning $100bn. Good luck getting that money hahah.

However, I could ideally rent 51% of the staked eth for an hour, for only $2mn (formula: 10^11 * 15% / (24 * 365); that's nothing!!). In this hour, I could give myself a few $bn worth of Ethereum, for a huge net profit.

I'm sure this is a well studied attack. How does Ethereum defend against it?