It all comes down to this:Although 21,000 Bitcoin inside an insurance fund, worth around 0.1% of the total Bitcoin supply may seem large, BitMEX cannot offer the same robust guarantees to winning traders, compared to those provided by traditional leveraged trading platforms. While the insurance fund has achieved a healthy size, it may not be large enough to give winning traders the confidence they need in the volatile and unpredictable bumpy road ahead in the crypto-currency space. Given such volatility, it’s not impossible that the fund is drained down to zero again.
33,749 BTC isn't
that much when you consider the potential volatility of BTC. Another event like this could happen at any time:
Auto-deleveraging has not occurred on the BitMEX Bitcoin perpetual swap contract since March 2017. In early March 2017, the SEC disapproved the Winklevoss’ application for the COIN Bitcoin ETF. On that day, the market dropped 30% in five minutes. The sharp price drop depleted the insurance fund entirely. Many XBTUSD shorts were ADL’d (Automatic Deleveraging) and their profits were capped.
Bitmex has never publicly used the fund for anything else, nor should they.