Actually I don't think I worried that the Airbnbs weren't going to be able to raise money. They were one of the top startups in their batch, and the top startups always manage to raise money. The reason I nagged Fred so persistently was that I thought he'd be a good match for them and I was annoyed that I couldn't convince him.

You still really think he did all of that only because of YC's ~6% stake in them?

Sometimes it can be advantageous for an investor to have a company crash and burn. If the company's main assets are likely to survive such an event without being destroyed, but be undervalued by people not familiar with the company, then an alert investor can buy those assets out of bankruptcy at a time when the people most invested in the company (founders, employees) have run out of money.

More prosaically, if you can delay the company's getting to break-even, they'll need more rounds of investment, which mean you can buy more of the company.

And then, of course, there are personal feuds. Remember what happened to Scout Electromedia? Their shutdown probably had as much to do with investors being pissed off about being ignored as with any actual rational assessment of their future prospects.