That's not actually true, back in the day Coinbase used Bitfinex. They were using them when Bitfinex got all that BTC stolen. Technically everyone, including Coinbase, lost assets in that hack. They were large and scary enough at the time to force Bitfinex to keep them whole instead of applying the 36% haircut, but I'd argue that amounts to recovery rather than failure to lose in the first place. [1, 2]
[1] https://www.kalzumeus.com/2019/10/28/tether-and-bitfinex