Can we explain this by saying many hedge funds are negatively correlated, along with survivor bias? This is a huge simplification, but consider for every four hedge fund managers, one goes long the market, another short the market, another long volatility and another short volatility. No matter what it's very likely one or two out of those four perform very well over one year. Start with enough hedge funds and throw…
The "beta" of finding funding or an acquirer is a funny kind of beta--it's highly unlikely that a great company will not get their first $1mm in funding because the VC world has just been deprived of $1b in assets allocated.
The cheapest way to short a startup is to bet on whatever establishment they're taking on. You could have shorted MSFT before they were public by buying IBM; if Big Iron kept on winning, you'd keep on getting your dividend checks. But startups are more akin to, e.g., long-shot CDS trades: the people betting against them get a predictable, incremental profit, or a massive, sudden loss.